| 1. |
- Andersson, Marta, et al.
(författare)
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Subjectivity (Re)visited : A Corpus Study of English Forward Causal Connectives in Different Domains of Spoken and Written Language
- 2021
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Ingår i: Discourse processes. - 0163-853X .- 1532-6950. ; 58:3, s. 260-292
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Tidskriftsartikel (refereegranskat)abstract
- Through a structured examination of four English causal discourse connectives, our article tackles a gap in the existing research, which focuses mainly on written language production, and entirely lacks attests on English spoken discourse. Given the alleged general nature of English connectives commonly emphasized in the literature, the underlying question of our investigation is the potential role of the connective phrases in marking the basic conceptual distinction between objective and subjective causal event types. To this end, our study combines a traditional corpus analysis with 'predictive' statistical modeling for subjectivity variables to investigate whether and how the tendencies found in the corpus depend on the systematic preferences of the language user to encode subjectivity via a discourse connective. Our findings suggest that while certain conceptual structures are quite fundamental to the usages of English connectives, the connectives per se do not seem to have a steady part in categorization of causal events. Rather, their role pertains to the level of intended explicitness bound to specific rhetorical purposes and contexts of use.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Björkström, Anders, et al.
(författare)
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A two-parametric class of predictors in multivariate regression
- 2007
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Ingår i: Journal of Chemometrics. - : Wiley. - 0886-9383 .- 1099-128X. ; 21:5-6, s. 215-226
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that a number of well-established multivariate regression methods for prediction are related in that they are special cases of basically one general procedure. We try a more general method based on this procedure with two metaparameters. In a simulation study, based on a latent structure model, we compare this method to ridge regression (RR), multivariate partial least squares regression (PLSR) and repeated univariate PLSR. For most types of data sets studied, all methods do approximately equally well. There are some cases where RR and least squares ridge regression (LSRR) yield larger errors than the other methods, and we conclude that one-factor methods are not adequate for situations where more than one latent variable are needed to describe the data. Among those based on latent variables, none of the methods tried is superior to the others in any obvious way.
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| 7. |
- Björkström, Anders, et al.
(författare)
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Continuum regression is not always continuous
- 1996
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Ingår i: Journal of The Royal Statistical Society Series B-statistical Methodology. - 1369-7412 .- 1467-9868. ; B 58:4, s. 703-710
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Tidskriftsartikel (refereegranskat)
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| 8. |
- Björkström, Anders, 1947-
(författare)
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Regression methods in multidimensional prediction and estimation
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In regression with near collinear explanatory variables, the least squares predictor has large variance. Ordinary least squares regression (OLSR) often leads to unrealistic regression coefficients. Several regularized regression methods have been proposed as alternatives. Well-known are principal components regression (PCR), ridge regression (RR) and continuum regression (CR). The latter two involve a continuous metaparameter, offering additional flexibility.For a univariate response variable, CR incorporates OLSR, PLSR, and PCR as special cases, for special values of the metaparameter. CR is also closely related to RR. However, CR can in fact yield regressors that vary discontinuously with the metaparameter. Thus, the relation between CR and RR is not always one-to-one. We develop a new class of regression methods, LSRR, essentially the same as CR, but without discontinuities, and prove that any optimization principle will yield a regressor proportional to a RR, provided only that the principle implies maximizing some function of the regressor's sample correlation coefficient and its sample variance. For a multivariate response vector we demonstrate that a number of well-established regression methods are related, in that they are special cases of basically one general procedure. We try a more general method based on this procedure, with two meta-parameters. In a simulation study we compare this method to ridge regression, multivariate PLSR and repeated univariate PLSR. For most types of data studied, all methods do approximately equally well. There are cases where RR and LSRR yield larger errors than the other methods, and we conclude that one-factor methods are not adequate for situations where more than one latent variable are needed to describe the data. Among those based on latent variables, none of the methods tried is superior to the others in any obvious way.
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| 9. |
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| 10. |
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| 11. |
- Bojarova, Jelena, et al.
(författare)
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Non-Gaussian state space models in decomposition of ice core time series in long and short time-scales
- 2010
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Ingår i: Environmetrics. - : Wiley. - 1180-4009 .- 1099-095X. ; 21:6, s. 562-587
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Tidskriftsartikel (refereegranskat)abstract
- Statistical modelling of six time series of geological ice core chemical data from Greenland is discussed. We decompose the total variation into long time-scale (trend) and short time-scale variations (fluctuations around the trend), and a pure noise component. Too heavy tails of the short-term variation makes a standard time-invariant linear Gaussian model inadequate. We try non-Gaussian state space models, which can be efficiently approximated by time-dependent Gaussian models. In essence, these time-dependent Gaussian models result in a local smoothing, in contrast to the global smoothing provided by the time-invariant model. To describe the mechanism of this local smoothing, we utilise the concept of a local variance function derived from a heavy-tailed density. The time-dependent error variance expresses the uncertainty about the dynamical development of the model state, and it controls the influence of observations on the estimates of the model state components. The great advantage of the derived time-dependent Gaussian model is that the Kalman filter and the Kalman smoother can be used as efficient computational tools for performing the variation decomposition. One of the main objectives of the study is to investigate how the distributional assumption on the model error component of the short time-scale variation affects the decomposition.
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| 12. |
- Bojarova, Jelena, 1971-
(författare)
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Toward Sequential Data Assimilation for NWP Models Using Kalman Filter Tools
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the meteorological data assimilation is to provide an initial field for Numerical Weather Prediction (NWP) and to sequentially update the knowledge about it using available observations. Kalman filtering is a robust technique for the sequential estimation of the unobservable model state based on the linear regression concept. In the iterative use together with Kalman smoothing, it can easily be extended to work powerfully in the non-Gaussian and/or non-linear framework. The huge dimensionality of the model state variable for high resolution NWP models (magnitude 108) makes it impossible with any explicit manipulations of the forecast error covariance matrix required for Kalman filter and Kalman smoother recursions. For NWP models the technical implementation of a Kalman filtering becomes the main challenge which provokes developments of novel data assimilation algorithms. This thesis is concerned with extensions of the Kalman filtering when the assumptions on linearity and Gaussianity of the state space model are violated. The research includes both theoretical studies of the properties of such extensions, within the framework of idealized small-dimensional models, and the development of the data assimilation algorithms for a full scale limited area high resolution NWP forecasting system. This thesis shows that non-Gaussian state space models can efficiently be approximated by a Gaussian state space model with an adaptively estimated variance of the stochastic forcing. That results in a type of local smoothing, in contrast to the global smoothing provided by Gaussian state space models. With regards to NWP models, the thesis shows that the sequential update of the uncertainty about the model state estimate is essential for efficient extraction of information from observations. The Ensemble Kalman filters can be used to represent both flow- and observation-network-dependent structures of the forecast error covariance matrix, in spite of a severe rank-deficiency of the Ensemble Kalman filters. As a culmination of this research the hybrid variational data assimilation has been developed on top of the HIRLAM variational data assimilation system. It provides the possibility of utilizing, during the data assimilation process, the error-of-the-day structure of the forecast error covariance, estimated from the ensemble of perturbations, at the same time as the full rank of the variational data assimilation is preserved.
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| 13. |
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| 14. |
- Carlson, Rolf, et al.
(författare)
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Gunnar Fant 1920-2009 In Memoriam
- 2009
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Ingår i: Phonetica. - : Walter de Gruyter GmbH. - 0031-8388 .- 1423-0321. ; 66:4, s. 249-250
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Tidskriftsartikel (refereegranskat)
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| 15. |
- Carlson, Rolf, et al.
(författare)
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Speech and music performance : parallels and contrasts
- 1989
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Ingår i: Contemporary Music Review. - 0749-4467 .- 1477-2256. ; 4, s. 389-402
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Tidskriftsartikel (refereegranskat)abstract
- Speech and music performance are two important systems for interhuman communication by means of acoustic signals. These signals must be adapted to the human perceptual and cognitive systems. Hence a comparitive analysis of speech and music performances is likely to shed light on these systems, particularly regarding basic requirements for acoustic communication. Two computer programs are compared, one for text-to-speech conversion and one for note-to-tone conversion. Similarities are found in the need for placing emphasis on unexpected elements, for increasing the dissimilarities between different categories, and for flagging structural constituents. Similarities are also found in the code chosen for conveying this information, e.g. emphasis by lengthening and constituent marking by final lengthening.
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| 16. |
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| 17. |
- Castensson, Anja, et al.
(författare)
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Decrease of serotonin receptor 2C in schizophrenia brains identified by high-resolution mRNA expression analysis
- 2003
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Ingår i: Biological Psychiatry. - 0006-3223 .- 1873-2402. ; 54:11, s. 1212-1221
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: RNA expression profiling can provide hints for the selection of candidate susceptibility genes, for formulation of hypotheses about the development of a disease, and/or for selection of candidate gene targets for novel drug development. We measured messenger RNA expression levels of 16 candidate genes in brain samples from 55 schizophrenia patients and 55 controls. This is the largest sample so far used to identify genes differentially expressed in schizophrenia brains. METHODS: We used a sensitive real-time polymerase chain reaction methodology and a novel statistical approach, including the development of a linear model of analysis of covariance type. RESULTS: We found two genes differentially expressed: monoamine oxidase B was significantly increased in schizophrenia brain (p =.001), whereas one of the serotonin receptor genes, serotonin receptor 2C, was significantly decreased (p =.001). Other genes, previously proposed to be differentially expressed in schizophrenia brain, were invariant in our analysis. CONCLUSIONS:The differential expression of serotonin receptor 2C is particularly relevant for the development of new atypical antipsychotic drugs. The strategy presented here is useful to evaluate hypothesizes for the development of the disease proposed by other investigators.
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| 18. |
- Castensson, Anja, et al.
(författare)
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Decrease of serotonin receptor 2C in schizophrenia brains identified by high-resolution mRNA expression analysis
- 2003
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Ingår i: Biological Psychiatry. - : Elsevier BV. - 0006-3223 .- 1873-2402. ; 54:11, s. 1212-1221
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Tidskriftsartikel (refereegranskat)abstract
- Background: RNA expression profiling can provide hints for the selection of candidate susceptibility genes, for formulation of hypotheses about the development of a disease, and/or for selection of candidate gene targets for novel drug development. We measured messenger RNA expression levels of 16 candidate genes in brain samples from 55 schizophrenia patients and 55 controls. This is the largest sample so far used to identify genes differentially expressed in schizophrenia brains.Methods: We used a sensitive real-time polymerase chain reaction methodology and a novel statistical approach, including the development of a linear model of analysis of covariance type.Results: We found two genes differentially expressed: monoamine oxidase B was significantly increased in schizophrenia brain (p = .001), whereas one of the serotonin receptor genes, serotonin receptor 2C, was significantly decreased (p = .001). Other genes, previously proposed to be differentially expressed in schizophrenia brain, were invariant in our analysis.Conclusions: The differential expression of serotonin receptor 2C is particularly relevant for the development of new atypical antipsychotic drugs. The strategy presented here is useful to evaluate hypothesizes for the development of the disease proposed by other investigators.
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| 19. |
- Eriksson, Olle, 1967-
(författare)
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Sensitivity and Uncertainty Analysis Methods : with Applications to a Road Traffic Emission Model
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is always a need to study the properties of complex input–output systems, properties that may be very difficult to determine. Two such properties are the output’s sensitivity to changes in the inputs and the output’s uncertainty if the inputs are uncertain.A system can be formulated as a model—a set of functions, equations and conditions that describe the system. We ultimately want to study and learn about the real system, but with a model that approximates the system well, we can study the model instead, which is usually easier. It is often easier to build a model as a set of combined sub-models, but good knowledge of each sub-model does not immediately lead to good knowledge of the entire model. Often, the most attractive approach to model studies is to write the model as computer software and study datasets generated by that software.Methods for sensitivity analysis (SA) and uncertainty analysis (UA) cannot be expected to be exactly the same for all models. In this thesis, we want to determine suitable SA and UA methods for a road traffic emission model, methods that can also be applied to any other model of similar structure. We examine parts of a well-known emission model and suggest a powerful data-generating tool. By studying generated datasets, we can examine properties in the model, suggest SA and UA methods and discuss the properties of these methods. We also present some of the results of applying the methods to the generated datasets.
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| 20. |
- Fetisova, Ekaterina
(författare)
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Evaluation of climate model simulations by means of statistical methods
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Evaluation of climate model simulations is a key issue within climate research. The statistical framework proposed by Sundberg et al., 2012, provides a theoretical underpinning of methods for evaluation of climate models by use of climateproxy data from the last millennium. In the present work, the statistical framework above is used to suggest several latent factor models of different complexity that can be used for estimating the amplitude of a forcing effect in aclimate model by comparison with the observed/reconstructed climate. The performance of the models is evaluated and compared in a pseudo-proxy experiment, in which the true unobservable temperature series is replaced by selected realizations of a climate simulation model. For different levels of added noise, different conclusions can be drawn. However, for realistic noise levels, we find that the simplest model, the just-identified two-indicator one-factor model, denoted j.i.FA(2,1), is a competitive alternative to models with more complicated structure. Moreover, we discover that the Fieller method of constructing confidence regions, associated with the j.i.FA(2,1)-model, outperforms the Wald confidence interval, which in most cases fails to provide sensible and interpretable conclusions about the climate model under consideration. Last but not least, the results indicate a good performance of the j.i.FA(2,1)-model even in the presence of heteroscedasticity.
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| 21. |
- Fetisova, Ekaterina, 1974-
(författare)
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Towards a flexible statistical modelling by latent factors for evaluation of simulated responses to climate forcings
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, using the principles of confirmatory factor analysis (CFA) and the cause-effect concept associated with structural equation modelling (SEM), a new flexible statistical framework for evaluation of climate model simulations against observational data is suggested. The design of the framework also makes it possible to investigate the magnitude of the influence of different forcings on the temperature as well as to investigate a general causal latent structure of temperature data. In terms of the questions of interest, the framework suggested here can be viewed as a natural extension of the statistical approach of 'optimal fingerprinting', employed in many Detection and Attribution (D&A) studies. Its flexibility means that it can be applied under different circumstances concerning such aspects as the availability of simulated data, the number of forcings in question, the climate-relevant properties of these forcings, and the properties of the climate model under study, in particular, those concerning the reconstructions of forcings and their implementation. It should also be added that although the framework involves the near-surface temperature as a climate variable of interest and focuses on the time period covering approximately the last millennium prior to the industrialisation period, the statistical models, included in the framework, can in principle be generalised to any period in the geological past as soon as simulations and proxy data on any continuous climate variable are available. Within the confines of this thesis, performance of some CFA- and SEM-models is evaluated in pseudo-proxy experiments, in which the true unobservable temperature series is replaced by temperature data from a selected climate model simulation. The results indicated that depending on the climate model and the region under consideration, the underlying latent structure of temperature data can be of varying complexity, thereby rendering our statistical framework, serving as a basis for a wide range of CFA- and SEM-models, a powerful and flexible tool. Thanks to these properties, its application ultimately may contribute to an increased confidence in the conclusions about the ability of the climate model in question to simulate observed climate changes.
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| 22. |
- Fetisova, Ekaterina, 1974-, et al.
(författare)
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Towards a flexible statistical modelling by latent factors for evaluation of simulated responses to climate forcings: Part I
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Evaluation of climate model simulations is a crucial task in climate research. In a work consisting of three parts, we propose a new statistical framework for evaluation of simulated responses to climate forcings, based on the concept of latent (unobservable) factors. Here, in Part I, we suggest several latent factor models of different complexity that can be used for evaluation of temperature data from climate model simulations against climate proxy data from the last millennium. Each factor model is developed for use with data from a single region, which can be of any size. To be able to test the hypotheses of interest, we have applied the technique of confirmatory factor analysis. We also elucidate the link between our factor models and the statistical methods used in Detection and Attribution (D\&A) studies. In particular, we demonstrate that our factor models can be used as an alternative approach to the methods used in D\&A studies. An additional advantage of their use is that they, in contrast to the commonly used D\&A methods, make it, in principle, possible to investigate whether the forcings of interest act additively or if any interaction effects exist.In Part II we investigate and illustrate the expansion of factor models to structural equation models, which permits the statistical modelling of more complicated climatological relationships. The performance of some of our statistical models suggested in Part I and Part is evaluated and compared in a numerical experiment, whose results are presented in Part III.
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| 23. |
- Fuchs, Dieter, et al.
(författare)
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Metronomic administration of the drug GMX1777, a cellular NAD synthesis inhibitor, results in neuroblastoma regression and vessel maturation without inducing drug resistance
- 2010
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Ingår i: International Journal of Cancer. - : Wiley. - 0020-7136 .- 1097-0215. ; 126:12, s. 2772-2789
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Tidskriftsartikel (refereegranskat)abstract
- High-risk neuroblastoma is a rapidly growing tumor with a survival rate below 50%. A new treatment strategy is to administer chemotherapeutic drugs metronomically, i.e. at lower doses and frequent intervals. The aim of the study was to investigate the effects of GMX1777, a chemotherapeutic drug affecting cellular energy metabolism, in a mouse model for high-risk neuroblastoma.Female SCID mice were injected s.c. with MYCN-amplified human neuroblastoma cells and randomized to either treatment with GMX1777 or vehicle. In some animals, treatment was discontinued allowing tumor relapse. Treatment response was evaluated using the Pediatric Preclinical Testing Program (PPTP). Immunohistochemistry and qRT-PCR was performed on tumor cryosections to investigate the microscopic and molecular changes in tumors in response to GMX1777.Despite an increase in vessel density, tumor regression and a high group response score according to PPTP criteria was induced by GMX1777 without inducing drug resistance. Treatment resulted in inhibition of tumor cell proliferation, vessel maturation, reduced hypoxia, increased infiltration of MHC class II negative macrophages and expansion of the non-vascular stromal compartment. Decreased stromal VEGF-A and PDGF-B mRNA in response to treatment together with the structural data suggest a "deactivation" or "silencing" of the tumor stroma as a paracrine entity.In conclusion, GMX1777 was highly efficient against high-risk neuroblastoma xenografts through modulation of both the tumor cell and stromal compartment.
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| 24. |
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| 25. |
- Gramming, Patricia, et al.
(författare)
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Relationship between changes in voice pitch and loudness
- 1988
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Ingår i: Journal of Voice. - 0892-1997 .- 1873-4588. ; 2:2, s. 118-126
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Tidskriftsartikel (refereegranskat)abstract
- Summary Changes in mean fundamental frequency accompanying changes in loudness of phonation are analyzed in 9 professional singers, 9 nonsingers, and 10 male and 10 female patients suffering from vocal functional dysfunction. The subjects read discursive texts with noise in earphones, and some also at voluntarily varied vocal loudness. The healthy subjects phonated as softly and as loudly as possible at various fundamental frequencies throughout their pitch ranges, and the resulting mean phonetograms are compared. Mean pitch was found to increase by about half-semitones per decibel sound level. Grossly, the subject groups gave similar results, although the singers changed voice pitch more than the nonsingers. The voice pitch changes may be explained as passive results of changes of subglottal pressure required for the sound level variation.
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| 26. |
- Gummesson, Sara, et al.
(författare)
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Lithic Raw Material Economy in the Mesolithic : Experimental Test of Edged Tool Efficiency and Durability in Bone Tool Production
- 2017
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Ingår i: Lithic Technology. - : Informa UK Limited. - 0197-7261 .- 2051-6185. ; 42:4, s. 140-154
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Tidskriftsartikel (refereegranskat)abstract
- The foundation of this paper is lithic economy with a focus on the actual use of different lithic raw materials for tasks at hand. Our specific focus is on the production of bone tools during the Mesolithic. The lithic and osseous assemblages from Strandvägen, Motala, in east-central Sweden provide the archaeological background for the study. Based on a series of experiments we evaluate the efficiency and durability of different tool edges of five lithic raw materials: Cambrian flint, Cretaceous flint, mylonitic quartz, quartz, and porphyry, each used to whittle bone. The results show that flint is the most efficient of the raw materials assessed. Thus, a non-local raw material offers complements of functional characteristics for bone working compared to locally available quartz and mylonitic quartz. This finding provides a new insight into lithic raw material distribution in the region, specifically for bone tool production on site.
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| 27. |
- Henningsson, Marcus, et al.
(författare)
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Sensor fusion a a tool to monitor dynamic dairy processes
- 2006
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Ingår i: Journal of Food Engineering. - : Elsevier BV. - 0260-8774 .- 1873-5770. ; 76:2, s. 154-162
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Tidskriftsartikel (refereegranskat)abstract
- A system for monitoring milk and fat concentration in a dynamic milk/water system by fusing information from several sensors was investigated. Standard instrumentation for food production was used, the sensors were a conductivity meter, a density meter and an optical instrument used to measure backscattered light. The system was applied to a dynamic mixing situation. Prediction error did not exceed 2% in the milk concentration and 0.1% fat in the total fat concentration. The applicability of the sensor fusion approach in field conditions was demonstrated by mounting the sensors in a dairy plant and monitoring the start-up of a pasteurizer.
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| 28. |
- Hind, Alistair, et al.
(författare)
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Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 2 : A pseudo-proxy study addressing the amplitude of solar forcing
- 2012
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Ingår i: Climate of the Past. - : European Geosciences Union (EGU). - 1814-9324 .- 1814-9332. ; 8:4, s. 1355-1365
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Tidskriftsartikel (refereegranskat)abstract
- The statistical framework of Part 1 (Sundberg et al., 2012), for comparing ensemble simulation surface temperature output with temperature proxy and instrumental records, is implemented in a pseudo-proxy experiment. A set of previously published millennial forced simulations (Max Planck Institute – COSMOS), including both "low" and "high" solar radiative forcing histories together with other important forcings, was used to define "true" target temperatures as well as pseudo-proxy and pseudo-instrumental series. In a global land-only experiment, using annual mean temperatures at a 30-yr time resolution with realistic proxy noise levels, it was found that the low and high solar full-forcing simulations could be distinguished. In an additional experiment, where pseudo-proxies were created to reflect a current set of proxy locations and noise levels, the low and high solar forcing simulations could only be distinguished when the latter served as targets. To improve detectability of the low solar simulations, increasing the signal-to-noise ratio in local temperature proxies was more efficient than increasing the spatial coverage of the proxy network. The experiences gained here will be of guidance when these methods are applied to real proxy and instrumental data, for example when the aim is to distinguish which of the alternative solar forcing histories is most compatible with the observed/reconstructed climate.
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| 29. |
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| 30. |
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| 31. |
- Lacerda, F., et al.
(författare)
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Modelling interactive language learning : a project presentation
- 2004
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Ingår i: Proceedings of The XVIIth Swedish Phonetics Conference, Fonetik 2004. - Stockholm University. ; , s. 60-63
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper describes a recently started inter-disciplinary research program aiming at inves-tigating and modelling fundamental aspects of the language acquisition process. The working hypothesis assumes that general purpose per-ception and memory processes, common to both human and other mammalian species, along with the particular context of initial adult-infant interaction, underlie the infant’s ability to progressively derive linguistic struc-ture implicitly available in the ambient lan-guage. The project is conceived as an interdis-ciplinary research effort involving the areas of Phonetics, Psychology and Speech recognition. Experimental speech perception techniques will be used at Dept. of Linguistics, SU, to investi-gate the development of the infant’s ability to derive linguistic information from situated con-nected speech. These experiments will be matched by behavioural tests of animal sub-jects, carried out at CMU, Pittsburgh, to dis-close the potential significance that recurrent multi-sensory properties of the stimuli may have for spontaneous category formation. Data from infant and child vocal productions as well as infant-adult interactions will also be col-lected and analyzed to address the possibility of a production-perception link. Finally, the data from the infant and animal studies will be inte-grated and tested in mathematical models of the language acquisition process, developed at TMH, KTH.
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| 32. |
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| 33. |
- Lashgari, Katarina, 1974-, et al.
(författare)
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Evaluation of simulated responses to climate forcings : a flexible statistical framework using confirmatory factor analysis and structural equation modelling – Part 1: Theory
- 2022
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Ingår i: Advances in Statistical Climatology, Meteorology and Oceanography. - : Copernicus GmbH. - 2364-3587. ; 8:2, s. 225-248
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Tidskriftsartikel (refereegranskat)abstract
- Evaluation of climate model simulations is a crucial task in climate research. Here, a new statistical framework is proposed for evaluation of simulated temperature responses to climate forcings against temperature reconstructions derived from climate proxy data for the last millennium. The framework includes two types of statistical models, each of which is based on the concept of latent (unobservable) variables: confirmatory factor analysis (CFA) models and structural equation modelling (SEM) models. Each statistical model presented is developed for use with data from a single region, which can be of any size. The ideas behind the framework arose partly from a statistical model used in many detection and attribution (D&A) studies. Focusing on climatological characteristics of five specific forcings of natural and anthropogenic origin, the present work theoretically motivates an extension of the statistical model used in D&A studies to CFA and SEM models, which allow, for example, for non-climatic noise in observational data without assuming the additivity of the forcing effects. The application of the ideas of CFA is exemplified in a small numerical study, whose aim was to check the assumptions typically placed on ensembles of climate model simulations when constructing mean sequences. The result of this study indicated that some ensembles for some regions may not satisfy the assumptions in question.
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| 34. |
- Moberg, Anders, et al.
(författare)
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Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium - Part 3 : Practical considerations, relaxed assumptions, and using tree-ring data to address the amplitude of solar forcing
- 2015
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 11:3, s. 425-448
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Tidskriftsartikel (refereegranskat)abstract
- A statistical framework for evaluation of climate model simulations by comparison with climate observations from instrumental and proxy data (part 1 in this series) is improved by the relaxation of two assumptions. This allows autocorrelation in the statistical model for simulated internal climate variability and enables direct comparison of two alternative forced simulations to test whether one fits the observations significantly better than the other. The extended framework is applied to a set of simulations driven with forcings for the pre-industrial period 1000-1849 CE and 15 tree-ring-based temperature proxy series. Simulations run with only one external forcing (land use, volcanic, small-amplitude solar, or large-amplitude solar) do not significantly capture the variability in the tree-ring data - although the simulation with volcanic forcing does so for some experiment settings. When all forcings are combined (using either the small- or large-amplitude solar forcing), including also orbital, greenhouse-gas and non-volcanic aerosol forcing, and additionally used to produce small simulation ensembles starting from slightly different initial ocean conditions, the resulting simulations are highly capable of capturing some observed variability. Nevertheless, for some choices in the experiment design, they are not significantly closer to the observations than when unforced simulations are used, due to highly variable results between regions. It is also not possible to tell whether the small-amplitude or large-amplitude solar forcing causes the multiple-forcing simulations to be closer to the reconstructed temperature variability. Proxy data from more regions and of more types, or representing larger regions and complementary seasons, are apparently needed for more conclusive results from model-data comparisons in the last millennium.
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| 35. |
- Norén, G. Niklas, et al.
(författare)
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A statistical methodology for drug–drug interaction surveillance
- 2008
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Ingår i: Statistics in Medicine. - : Wiley. - 0277-6715 .- 1097-0258. ; 27:16, s. 3057-3070
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Tidskriftsartikel (refereegranskat)abstract
- Interaction between drug substances may yield excessive risk of adverse drug reactions (ADRs) when two drugs are taken in combination. Collections of individual case safety reports (ICSRs) related to suspected ADR incidents in clinical practice have proven to be very useful in post-marketing surveillance for pairwise drug–ADR associations, but have yet to reach their full potential for drug–drug interaction surveillance. In this paper, we implement and evaluate a shrinkage observed-to-expected ratio for exploratory analysis of suspected drug–drug interaction in ICSR data, based on comparison with an additive risk model. We argue that the limited success of previously proposed methods for drug–drug interaction detection based on ICSR data may be due to an underlying assumption that the absence of interaction is equivalent to having multiplicative risk factors. We provide empirical examples of established drug–drug interaction highlighted with our proposed approach that go undetected with logistic regression. A database wide screen for suspected drug–drug interaction in the entire WHO database is carried out to demonstrate the feasibility of the proposed approach. As always in the analysis of ICSRs, the clinical validity of hypotheses raised with the proposed method must be further reviewed and evaluated by subject matter experts.
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| 36. |
- Norén, G. Niklas, 1977-
(författare)
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Statistical methods for knowledge discovery in adverse drug reaction surveillance
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Collections of individual case safety reports are the main resource for early discovery of unknown adverse reactions to drugs once they have been introduced to the general public. The data sets involved are complex and based on voluntary submission of reports, but contain pieces of very important information. The aim of this thesis is to propose computationally feasible statistical methods for large-scale knowledge discovery in these data sets. The main contributions are a duplicate detection method that can reliably identify pairs of unexpectedly similar reports and a new measure for highlighting suspected drug-drug interaction. Specifically, we extend the hit-miss model for database record matching with a hit-miss mixture model for scoring numerical record fields and a new method to compensate for strong record field correlations. The extended hit-miss model is implemented for the WHO database and demonstrated to be useful in real world duplicate detection, despite the noisy and incomplete information on individual case safety reports. The Information Component measure of disproportionality has been in routine use since 1998 to screen the WHO database for excessive adverse drug reaction reporting rates. Here, it is further refined. We introduce improved credibility intervals for rare events, post-stratification adjustment for suspected confounders and an extension to higher order associations that allows for simple but robust screening for potential risk factors. A new approach to identifying reporting patterns indicative of drug-drug interaction is also proposed. Finally, we describe how imprecision estimates specific to each prediction of a Bayes classifier may be obtained with the Bayesian bootstrap. Such case-based imprecision estimates allow for better prediction when different types of errors have different associated loss, with a possible application in combining quantitative and clinical filters to highlight drug-ADR pairs for clinical review.
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| 37. |
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| 38. |
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| 39. |
- Rydén, Jesper, et al.
(författare)
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Willy Feller vid Stockholms högskola, 1934–1939 : En gigant inom sannolikhetsteorin på svensk mark
- 2021
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Ingår i: Qvintense. - 2000-1819. ; 2021:2, s. 4-8
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Harald Cramér utnämndes 1929 till professor i forsäkringsmatematik och matematisk statistik vid Stockholms högskola. Efter nagra år hade han ett eget institut, Institutet for forsäkringsmatematik och matematisk statistik, med egna lokaler vid Odengatan, och 1-2 anstallda amanuenser. Där bedrevs en livlig verksamhet.Cramér hade ett brett kontakt nät bland stora namn inom sannolikhetsteorin. I hans outgivna memoarer, "Korta minnen fran ett långt liv", kan man läsa om nära kontakter med t.ex. Lévy och Féechet i Paris. I Institutets seminarieserie märks internationella namn som t.ex. Theodore (Ted) W. Anderson, Jerzy Neyman - och från 1934 en begåvad ung matematiker vid namn Willy Feller, som gästade Institutet under nära fem års tid.Det är Feller som är ämnet för var uppsats, en sedermera berömd probabilist, inte minst känd för sina två böcker i ämnet.
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| 40. |
- Salnikov, Alexei V, et al.
(författare)
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Lowering of tumor interstitial fluid pressure specifically augments efficacy of chemotherapy
- 2003
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Ingår i: The FASEB Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 17:12, s. 1756-1758
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Tidskriftsartikel (refereegranskat)abstract
- Chemotherapy of solid tumors is presently largely ineffective at dosage levels that are compatible with survival of the patient. Here, it is argued that a condition of raised interstitial fluid pressure (IFP) that can be observed in many tumors is a major factor in preventing optimal access of systemically administered chemotherapeutic agents. Using prostaglandin E1-methyl ester (PGE1), which is known transiently to reduce IFP, it was shown that 5-fluorouracil (5-FU) caused significant growth inhibition on two experimental tumors in rats but only after administration of PGE1. Furthermore, timing experiments showed that only in the period in which IFP is reduced did 5-FU have an antitumor effect. These experiments uniquely demonstrate a clear and, according to the starting hypothesis, logical, synergistic effect of PGE1 and 5-FU that offers hope for better treatment of many tumors in which raised IFP is likely to be inhibiting optimal results with water-soluble cancer chemotherapeutic agents.
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| 41. |
- Sigurd, Bengt, et al.
(författare)
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Magritte, music and methods of language description
- 1991
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Ingår i: Music, Language, Speech and Brain : Proceedings of an International Symposium at the Wenner-Gren Center, Stockholm, 5–8 September 1990 - Proceedings of an International Symposium at the Wenner-Gren Center, Stockholm, 5–8 September 1990. - 0083-7989. - 9780333564295 - 9781349126729 - 9781349126705 ; 59, s. 57-67
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Konferensbidrag (refereegranskat)
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| 42. |
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| 43. |
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| 44. |
- Sundberg, Rolf
(författare)
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A classical dataset from Williams, and its role in the study of supersaturated designs.
- 2008
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Ingår i: Journal of Chemometrics. ; 22, s. 436-440
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Tidskriftsartikel (refereegranskat)abstract
- A Plackett–Burman type dataset from a paper by Williams (1968), with 28 observations and 24 two-level factors, has become a standard dataset for illustrating construction (by halving) of supersaturated designs (SSDs) and for a corresponding data analysis. The aim here is to point out that for several reasons this is an unfortunate situation. The original paper by Williams contains several errors and misprints. Some are in the design matrix, which will here be reconstructed, but worse is an outlier in the response values, which can be observed when data are plotted against the dominating factor. In addition, the data should better be analysed on log-scale than on original scale. The implications of the outlier for SSD analysis are drastic, and it will be concluded that the data should be used for this purpose only if the outlier is properly treated (omitted or modified).
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| 45. |
- Sundberg, Rolf, 1942-
(författare)
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A Note on “Shaved Dice” Inference
- 2018
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Ingår i: American Statistician. - : Informa UK Limited. - 0003-1305 .- 1537-2731. ; 72:2, s. 155-157
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Tidskriftsartikel (refereegranskat)abstract
- Two dice are rolled repeatedly, only their sum is registered. Have the two dice been shaved, so two of the six sides appear more frequently? Pavlides and Perlman discussed this somewhat complicated type of situation through curved exponential families. Here, we contrast their approach by regarding data as incomplete data from a simple exponential family. The latter, supplementary approach is in some respects simpler, it provides additional insight about the relationships among the likelihood equation, the Fisher information, and the EM algorithm, and it illustrates the information content in ancillary statistics.
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| 46. |
- Sundberg, Rolf, 1942-
(författare)
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Chemometrics
- 2011
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Ingår i: International Encyclopedia of Statistical Science. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642048975 - 9783642048982 - 9783642049163 ; , s. 240-242
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Bokkapitel (refereegranskat)
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| 47. |
- Sundberg, Rolf, 1942-
(författare)
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Collinearity
- 2002
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Ingår i: Encyclopedia of Environmetrics. - Chichester : John Wiley & Sons. - 0471899976 ; , s. 365-366
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Bokkapitel (refereegranskat)
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| 48. |
- Sundberg, Rolf, 1942-, et al.
(författare)
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Exploratory factor analysis-Parameter estimation and scores prediction with high-dimensional data
- 2016
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Ingår i: Journal of Multivariate Analysis. - : Elsevier BV. - 0047-259X .- 1095-7243. ; 148, s. 49-59
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Tidskriftsartikel (refereegranskat)abstract
- In an approach aiming at high-dimensional situations, we first introduce a distribution-free approach to parameter estimation in the standard random factor model, that is shown to lead to the same estimating equations as maximum likelihood estimation under normality. The derivation is considerably simpler, and works equally well in the case of more variables than observations (p>n). We next concentrate on the latter case and show results of type:• Albeit factor loadings and specific variances cannot be precisely estimated unless n is large, this is not needed for the factor scores to be precise, but only that p is large;• A classical fixed point iteration method can be expected to converge safely and rapidly, provided p is large. A microarray data set, with p=2000 and n=22, is used to illustrate this theoretical result.
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| 49. |
- Sundberg, Rolf, 1942-
(författare)
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Exponential Family Models
- 2011
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Ingår i: International Encyclopedia of Statistical Science. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642048975 - 9783642048982 - 9783642049163 ; , s. 490-493
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Bokkapitel (refereegranskat)
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| 50. |
- Sundberg, Rolf, 1942-
(författare)
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Flat and multimodal likelihoods and model lack of fit in curved exponential families
- 2010
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Ingår i: Scandinavian Journal of Statistics. - : Wiley. - 0303-6898 .- 1467-9469. ; 37:4, s. 632-643
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that curved exponential families can have multimodal likelihoods. We investigate the relationship between flat or multimodal likelihoods and model lack of fit, the latter measured by the score (Rao) test statistic of the curved model as embedded in the corresponding full model. When data yield a locally flat or convex likelihood (root of multiplicity >1, terrace point, saddle point, local minimum), we provide a formula for in such points, or a lower bound for it. The formula is related to the statistical curvature of the model, and it depends on the amount of Fisher information. We use three models as examples, including the Behrens-Fisher model, to see how a flat likelihood, etc. by itself can indicate a bad fit of the model. The results are related (dual) to classical results by Efron from 1978.
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