| 1. |
- Bengtsson, Boel, et al.
(författare)
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Perimetric probability maps to separate change caused by glaucoma from that caused by cataract
- 1997
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Ingår i: Acta Ophthalmologica Scandinavica. - 1395-3907. ; 75:2, s. 184-188
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Tidskriftsartikel (refereegranskat)abstract
- We describe a new method for analysis of change in glaucomatous visual fields with the object to differentiate between changes caused by glaucoma from those caused by cataract, New pattern deviation change probability maps were developed from a prospectively collected glaucoma material and designed to be sensitive to changes in localized field loss, but to be unaffected by media-induced perimetric change. We compared the new change probability maps with the commercially available total deviation change probability maps in series of Humphrey perimetric tests in a glaucoma material of 43 eyes of 35 patients, who had undergone cataract surgery, When using the total deviation maps, considerable differences were seen between fields obtained before and after cataract surgery. Much smaller differences were seen when using the new change probability maps, that almost eliminated the common and disturbing effect of increasing cataract, This new tool could be of considerable help in differentiation between progressive glaucomatous visual field loss and deterioration caused by increasing media opacities.
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| 2. |
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| 3. |
- Johansson, Mikael, et al.
(författare)
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Memory for perceived and imagined pictures : an event-related potential study
- 2002
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Ingår i: Neuropsychologia, vol. 40, no. 7. - : Elsevier. ; 40:7, s. 986-1002
-
Konferensbidrag (refereegranskat)abstract
- Event-related potentials (ERPs) and behavioural measures were used to investigate recognition memory and source-monitoring judgements about previously perceived and imagined pictures. At study, word labels of common objects were presented. Half of these were followed by a corresponding picture and the other half by an empty frame, signalling to the participants to mentally visualise an image. At test, participants in a source-monitoring task made a three-way discrimination between new words and words corresponding to previously perceived and imagined pictures. Participants in an old/new-recognition task indicated whether test words were previously presented or not. In both tasks, correctly identified old items elicited more positive-going ERPs than correctly judged new items. This widely distributed old/new effect was found to have an earlier onset and to be of a greater magnitude for imagined than for perceived items. Task (source versus item-memory) affected the old/new effects over prefrontal areas and the reaction times to remembered old items. The present findings are consistent with the view that a greater amount, or a different type, of information is necessary for accurate source-memory judgements than for correct recognition, and moreover, that different types of source-specifying information revive at different rates. In addition, the results add weight to the view that the late widespread ERP-old/new effect is sensitive to the quality or the amount of information retrieved from memory.
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| 4. |
- Joshi, Peter K, et al.
(författare)
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Directional dominance on stature and cognition in diverse human populations
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 523:7561, s. 459-462
-
Tidskriftsartikel (refereegranskat)abstract
- Homozygosity has long been associated with rare, often devastating, Mendelian disorders, and Darwin was one of the first to recognize that inbreeding reduces evolutionary fitness. However, the effect of the more distant parental relatedness that is common in modern human populations is less well understood. Genomic data now allow us to investigate the effects of homozygosity on traits of public health importance by observing contiguous homozygous segments (runs of homozygosity), which are inferred to be homozygous along their complete length. Given the low levels of genome-wide homozygosity prevalent in most human populations, information is required on very large numbers of people to provide sufficient power. Here we use runs of homozygosity to study 16 health-related quantitative traits in 354,224 individuals from 102 cohorts, and find statistically significant associations between summed runs of homozygosity and four complex traits: height, forced expiratory lung volume in one second, general cognitive ability and educational attainment (P < 1 × 10(-300), 2.1 × 10(-6), 2.5 × 10(-10) and 1.8 × 10(-10), respectively). In each case, increased homozygosity was associated with decreased trait value, equivalent to the offspring of first cousins being 1.2 cm shorter and having 10 months' less education. Similar effect sizes were found across four continental groups and populations with different degrees of genome-wide homozygosity, providing evidence that homozygosity, rather than confounding, directly contributes to phenotypic variance. Contrary to earlier reports in substantially smaller samples, no evidence was seen of an influence of genome-wide homozygosity on blood pressure and low density lipoprotein cholesterol, or ten other cardio-metabolic traits. Since directional dominance is predicted for traits under directional evolutionary selection, this study provides evidence that increased stature and cognitive function have been positively selected in human evolution, whereas many important risk factors for late-onset complex diseases may not have been.
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| 5. |
- Lindgren, Georg, et al.
(författare)
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Non-traditional stochastic models for ocean waves
- 2010
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Ingår i: The European Physical Journal. Special Topics. - : Springer Science and Business Media LLC. - 1951-6355 .- 1951-6401. ; 185, s. 209-224
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Forskningsöversikt (refereegranskat)abstract
- We present two flexible stochastic models for 2D and 3D ocean waves with potential to reproduce severe and non-homogeneous sea conditions. The first family consists of generalized Lagrange models for the movements of individual water particles. These models can generate crest-trough and front-back statistically asymmetric waves, with the same degree of asymmetry as measured ocean waves. They are still in the Gaussian family and it is possible to calculate different slope distributions exactly from a wave energy spectrum. The second model is a random field model that is generated by a nested stochastic partial differential equation. This model can be adapted to spatially non-homogeneous sea conditions and it can approximate standard wave spectra. One advantage with this model is that Hilbert space approximations can be used to obtain computationally efficient representations with Markov-type properties that facilitate the use of sparse matrix techniques in simulation and estimation.
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| 6. |
- Lindgren, Georg, et al.
(författare)
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Stochastic asymmetry properties of 3D Gauss-Lagrange ocean waves with directional spreading
- 2011
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Ingår i: Stochastic Models. - : Informa UK Limited. - 1532-6349 .- 1532-4214. ; 27:3, s. 490-520
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Tidskriftsartikel (refereegranskat)abstract
- In the stochastic Lagrange model for ocean waves the vertical and horizontal location of surface water particles are modeled as correlated Gaussian processes. In this article we investigate the statistical properties of wave characteristics related to wave asymmetry in the 3D Lagrange model. We present a modification of the original Lagrange model that can produce front-back asymmetry both of the space waves, i.e. observation of the sea surface at a fixed time, and of the time waves, observed at a fixed measuring station. The results, which are based on a multivariate form of Rice’s formula for the expected number of level crossings, are given in the form of the cumulative distribution functions for the slopes observed either by asynchronous sampling in space, or at synchronous sampling at upcrossings and down-crossings, respectively, of a specified fixed level. The theory is illustrated in a numerical section, showing how the degree of wave asymmetry depends on the directional spectral spreading and on the mean wave direction. It is seen that the asymmetry is more accentuated for high waves, a fact that may be of importance in safety analysis of capsizing risk.
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| 7. |
- Lindgren, M., et al.
(författare)
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Restitution of neurophysiological functions, performance, and subjective symptoms after moderate insulin-induced hypoglycaemia in non-diabetic men
- 1996
-
Ingår i: Diabetic Medicine. - : Wiley-Blackwell. - 0742-3071 .- 1464-5491. ; 13:3, s. 218-25
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Tidskriftsartikel (refereegranskat)abstract
- The restoration of cognitive function was studied in 10 healthy men aged 26 years (25.5 +/- 1.2 years; mean +/- SD) after insulin-induced hypoglycaemia (arterialized blood glucose 2.5 +/- 0.4 mmol l-1) for 62 +/- 8 min. Another group of six men participated in a single blind sham study for comparison. The hypoglycaemic event caused a significant increase (p = 0.006) in serum adrenaline levels. Ratings of adrenergically mediated symptoms increased during hypoglycaemia (p = 0.006), as did neuroglycopenic symptoms (p = 0.002), although neuroglycopenia ratings increased in both studies. During hypoglycaemia, P300 amplitudes in a relatively demanding visual search task decreased (p = 0.02), whereas easier tasks were unaffected. The amplitudes were restored after 40 min of normoglycaemia. Reaction time deteriorated after restoration of normoglycaemia, suggesting an effect of hypoglycaemia on learning. Thus, hypoglycaemia at a blood glucose level that is common among patients treated with insulin causes clear cognitive dysfunction, although restoration of the cognitive dysfunction to normal was fast.
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| 8. |
- Locke, Adam E, et al.
(författare)
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Genetic studies of body mass index yield new insights for obesity biology.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 197-401
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Tidskriftsartikel (refereegranskat)abstract
- Obesity is heritable and predisposes to many diseases. To understand the genetic basis of obesity better, here we conduct a genome-wide association study and Metabochip meta-analysis of body mass index (BMI), a measure commonly used to define obesity and assess adiposity, in up to 339,224 individuals. This analysis identifies 97 BMI-associated loci (P < 5 × 10(-8)), 56 of which are novel. Five loci demonstrate clear evidence of several independent association signals, and many loci have significant effects on other metabolic phenotypes. The 97 loci account for ∼2.7% of BMI variation, and genome-wide estimates suggest that common variation accounts for >20% of BMI variation. Pathway analyses provide strong support for a role of the central nervous system in obesity susceptibility and implicate new genes and pathways, including those related to synaptic function, glutamate signalling, insulin secretion/action, energy metabolism, lipid biology and adipogenesis.
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| 9. |
- Shungin, Dmitry, et al.
(författare)
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New genetic loci link adipose and insulin biology to body fat distribution.
- 2015
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 187-378
-
Tidskriftsartikel (refereegranskat)abstract
- Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms.
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| 10. |
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| 11. |
- Baldetorp, Bo, et al.
(författare)
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Statistical evaluation of cell kinetic data from DNA flow cytometry (FCM) by the EM algorithm
- 1989
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Ingår i: Cytometry. - : Wiley. - 0196-4763 .- 1097-0320. ; 10:6, s. 695-705
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Tidskriftsartikel (refereegranskat)abstract
- Flow cytometric DNA measurements yield the amount of DNA for each of a large number of cells. A DNA histogram normally consists of a mixture of one or more constellations of G0/G1-, S-, G2/M-phase cells, together with internal standards, debris, background noise, and one or more populations of clumped cells. We have modelled typical DNA histograms as a mixed distribution with Gaussian densities for the G0/G1 and G2/M phases, an S-phase density, assumed to be uniform between the G0/G1 and G2/M peaks, observed with a Gaussian error, and with Gaussian densities for standards of chicken and trout red blood cells. The debris is modelled as a truncated exponential distribution, and we also have included a uniform background noise distribution over the whole observation interval. We have explored a new approach for maximum-likelihood analyses of complex DNA histograms by the application of the EM algorithm. This algorithm was used for four observed DNA histograms of varying complexity. Our results show that the algorithm works very well, and it converges to reasonable values for all parameters. In simulations from the estimated models, we have investigated bias, variance, and correlations of the estimates.
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| 12. |
- Beckman, Stig-Inge, et al.
(författare)
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Alarm characteristics for a flood warning system with deterministic components
- 1990
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Ingår i: Journal of Time Series Analysis. - : Wiley. - 0143-9782 .- 1467-9892. ; 11:1, s. 1-18
-
Tidskriftsartikel (refereegranskat)abstract
- A method for evaluating a predictor-based alarm system is studied in this paper. The predictor is composed of a deterministic component reflecting external information and a statistically based component for the error between the measurements and the external predictor. The aim of the predictor study is twofold: it is a means of interpreting the connections between the alarm and the catastrophe, and it can be used to select suitable alarm levels. As an application, the performance of a water-level predictor as part of a flood warning system has been evaluated. The result of this analysis shows that an alarm system which operates when the predictor reaches a certain level will tend to give either too many alarms or alarms that are out of phase with the catastrophe.''
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| 13. |
- Berndt, Sonja I., et al.
(författare)
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Genome-wide meta-analysis identifies 11 new loci for anthropometric traits and provides insights into genetic architecture
- 2013
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 45:5, s. 501-U69
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Tidskriftsartikel (refereegranskat)abstract
- Approaches exploiting trait distribution extremes may be used to identify loci associated with common traits, but it is unknown whether these loci are generalizable to the broader population. In a genome-wide search for loci associated with the upper versus the lower 5th percentiles of body mass index, height and waist-to-hip ratio, as well as clinical classes of obesity, including up to 263,407 individuals of European ancestry, we identified 4 new loci (IGFBP4, H6PD, RSRC1 and PPP2R2A) influencing height detected in the distribution tails and 7 new loci (HNF4G, RPTOR, GNAT2, MRPS33P4, ADCY9, HS6ST3 and ZZZ3) for clinical classes of obesity. Further, we find a large overlap in genetic structure and the distribution of variants between traits based on extremes and the general population and little etiological heterogeneity between obesity subgroups.
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| 14. |
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| 15. |
- Chu, Audrey Y, et al.
(författare)
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Multiethnic genome-wide meta-analysis of ectopic fat depots identifies loci associated with adipocyte development and differentiation
- 2017
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 49:1, s. 125-130
-
Tidskriftsartikel (refereegranskat)abstract
- Variation in body fat distribution contributes to the metabolic sequelae of obesity. The genetic determinants of body fat distribution are poorly understood. The goal of this study was to gain new insights into the underlying genetics of body fat distribution by conducting sample-size-weighted fixed-effects genome-wide association meta-analyses in up to 9,594 women and 8,738 men of European, African, Hispanic and Chinese ancestry, with and without sex stratification, for six traits associated with ectopic fat (hereinafter referred to as ectopic-fat traits). In total, we identified seven new loci associated with ectopic-fat traits (ATXN1, UBE2E2, EBF1, RREB1, GSDMB, GRAMD3 and ENSA; P < 5 × 10(-8); false discovery rate < 1%). Functional analysis of these genes showed that loss of function of either Atxn1 or Ube2e2 in primary mouse adipose progenitor cells impaired adipocyte differentiation, suggesting physiological roles for ATXN1 and UBE2E2 in adipogenesis. Future studies are necessary to further explore the mechanisms by which these genes affect adipocyte biology and how their perturbations contribute to systemic metabolic disease.
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| 16. |
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| 17. |
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| 18. |
- Do, Ron, et al.
(författare)
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Common variants associated with plasma triglycerides and risk for coronary artery disease
- 2013
-
Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 45:11, s. 1345-
-
Tidskriftsartikel (refereegranskat)abstract
- Triglycerides are transported in plasma by specific triglyceride-rich lipoproteins; in epidemiological studies, increased triglyceride levels correlate with higher risk for coronary artery disease (CAD). However, it is unclear whether this association reflects causal processes. We used 185 common variants recently mapped for plasma lipids (P < 5 x 10(-8) for each) to examine the role of triglycerides in risk for CAD. First, we highlight loci associated with both low-density lipoprotein cholesterol (LDL-C) and triglyceride levels, and we show that the direction and magnitude of the associations with both traits are factors in determining CAD risk. Second, we consider loci with only a strong association with triglycerides and show that these loci are also associated with CAD. Finally, in a model accounting for effects on LDL-C and/or high-density lipoprotein cholesterol (HDL-C) levels, the strength of a polymorphism's effect on triglyceride levels is correlated with the magnitude of its effect on CAD risk. These results suggest that triglyceride-rich lipoproteins causally influence risk for CAD.
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| 19. |
- Evangelou, Evangelos, et al.
(författare)
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Genetic analysis of over 1 million people identifies 535 new loci associated with blood pressure traits.
- 2018
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 50:10, s. 1412-1425
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Tidskriftsartikel (refereegranskat)abstract
- High blood pressure is a highly heritable and modifiable risk factor for cardiovascular disease. We report the largest genetic association study of blood pressure traits (systolic, diastolic and pulse pressure) to date in over 1 million people of European ancestry. We identify 535 novel blood pressure loci that not only offer new biological insights into blood pressure regulation but also highlight shared genetic architecture between blood pressure and lifestyle exposures. Our findings identify new biological pathways for blood pressure regulation with potential for improved cardiovascular disease prevention in the future.
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| 20. |
- Felkel, Sabine, et al.
(författare)
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The horse Y chromosome as an informative marker for tracing sire lines
- 2019
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Analysis of the Y chromosome is the best-established way to reconstruct paternal family history in humans. Here, we applied fine-scaled Y-chromosomal haplotyping in horses with biallelic markers and demonstrate the potential of our approach to address the ancestry of sire lines. We de novo assembled a draft reference of the male-specific region of the Y chromosome from Illumina short reads and then screened 5.8 million basepairs for variants in 130 specimens from intensively selected and rural breeds and nine Przewalski's horses. Among domestic horses we confirmed the predominance of a young'crown haplogroup' in Central European and North American breeds. Within the crown, we distinguished 58 haplotypes based on 211 variants, forming three major haplogroups. In addition to two previously characterised haplogroups, one observed in Arabian/Coldblooded and the other in Turkoman/Thoroughbred horses, we uncovered a third haplogroup containing Iberian lines and a North African Barb Horse. In a genealogical showcase, we distinguished the patrilines of the three English Thoroughbred founder stallions and resolved a historic controversy over the parentage of the horse 'Galopin', born in 1872. We observed two nearly instantaneous radiations in the history of Central and Northern European Y-chromosomal lineages that both occurred after domestication 5,500 years ago.
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| 21. |
- Figueiredo, Bruno, 1981-, et al.
(författare)
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Review: The state-of-art of sparse channel models and their applicability to performance assessment of radioactive waste repositories in fractured crystalline formations
- 2016
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 24:7, s. 1607-1622
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Laboratory and field experiments done on fractured rock show that flow and solute transport often occur along flow channels. ‘Sparse channels’ refers to the case where these channels are characterised by flow in long flow paths separated from each other by large spacings relative to the size of flow domain. A literature study is presented that brings together information useful to assess whether a sparse-channel network concept is an appropriate representation of the flow system in tight fractured rock of low transmissivity, such as that around a nuclear waste repository in deep crystalline rocks. A number of observations are made in this review. First, conventional fracture network models may lead to inaccurate results for flow and solute transport in tight fractured rocks. Secondly, a flow dimension of 1, as determined by the analysis of pressure data in well testing, may be indicative of channelised flow, but such interpretation is not unique or definitive. Thirdly, in sparse channels, the percolation may be more influenced by the fracture shape than the fracture size and orientation but further studies are needed. Fourthly, the migration of radionuclides from a waste canister in a repository to the biosphere may be strongly influenced by the type of model used (e.g. discrete fracture network, channel model). Fifthly, the determination of appropriateness of representing an in situ flow system by a sparse-channel network model needs parameters usually neglected in site characterisation, such as the density of channels or fracture intersections.
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| 22. |
- Geier, Joel E., et al.
(författare)
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Simplified representative models for long-term flow and advective transport in fractured crystalline bedrock
- 2019
-
Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 27:2, s. 595-614
-
Tidskriftsartikel (refereegranskat)abstract
- Simplified representative models (SRMs) of the hydrogeological system at radioactive-waste repository sites are presented and demonstrated to give useful predictions of the key hydrogeological factors affecting long-term safety. The SRM is constructed from complex site-descriptive models, which have been developed to be consistent with detailed site information and data from short-term (with duration of days, weeks, up to months) field experiments, by keeping elements that are important for long-term predictions into thousands of years and simplifying features of less importance. The simplified approach relies only on fundamental hydrogeological principles and the mathematics can be kept relatively simple. The purpose of SRM is to provide a means of verifying predictions from complex numerical models, with an approach that is easy to evaluate and allows transparent evaluation of factors influencing long-term results. The approach is applied to evaluations of sites for two repositories in fractured crystalline bedrock in Sweden: one for spent nuclear fuel rod assemblies and one for waste with lower levels of radioactivity. The results indicate that the SRMs are able to yield results similar to those of calculations based on much more complex models. Further, the approach allows an evaluation of additional sources of uncertainty that are difficult or expensive to conduct with the complex models. These capabilities make SRMs a very useful and transparent tool for regulatory review.
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| 23. |
- Grage, Halfdan, et al.
(författare)
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Level crossing prediction with neural networks
- 2010
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Ingår i: Methodology and Computing in Applied Probability. - : Springer Science and Business Media LLC. - 1573-7713 .- 1387-5841. ; 63:Online First, s. 623-645
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Tidskriftsartikel (refereegranskat)abstract
- A level crossing predictor or alarm system with prediction horizon k is said to be optimal if it, at time t detects that an upcrossing will occur at time t + k, with a certain high probability and simultaneously gives a minimum number of false alarms. For a Gaussian stationary process, the optimal level crossing predictor can be explicitly specified in terms of the predicted value of the process itself and of its derivative. To the authors knowledge this simple optimal solution has not been used to any substantial degree. In this paper it is shown how a neural network can be trained to approximate an optimal alarm system arbitrarily well. As in other methods of parametrization, the choice of model structure, as well as an appropriate representation of data, are crucial for a good result. Comparative studies are presented for two Gaussian ARMA-processes, for which the optimal predictor can be derived theoretically. These studies confirm that a properly trained neural network can indeed approximate an optimal alarm system quite well – with due attention paid to the problems of model structure and representation of data. The technique is also tested on a strongly non-Gaussian Duffing process with satisfactory results.
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| 24. |
- Guttorp, Peter, et al.
(författare)
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Karl Pearson and the Scandinavian school of statistics
- 2009
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Ingår i: International Statistical Review. - : Wiley. - 1751-5823 .- 0306-7734. ; 77:1, s. 64-71
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Forskningsöversikt (refereegranskat)abstract
- The relationship between Karl Pearson and the Scandinavian statisticians was more of a competitive than a collaborative nature. We describe the leading statisticians and stochasticists of the Scandinavian school, and relate some of their work to the work of Pearson.
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| 25. |
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| 26. |
- Heijl, Anders, et al.
(författare)
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On weighted visual field indices
- 1992
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Ingår i: Graefe's Archive for Clinical and Experimental Ophthalmology. - 1435-702X. ; 230:4, s. 397-400
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Tidskriftsartikel (refereegranskat)
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| 27. |
- Heijl, Anders, et al.
(författare)
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The effect of perimetric experience in normal subjets
- 1989
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Ingår i: Archives of Ophthalmology. - 0003-9950. ; 107:1, s. 81-86
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Tidskriftsartikel (refereegranskat)abstract
- Two groups of normal subjects were submitted to repeated automated static threshold perimetry. Perimetric results were strongly affected by the level of experience in some subjects; in the majority, however, the effect of experience was small. Initial field tests often showed high numbers of depressed points. Sensitivity increased with perimetric training, particularly between the first sessions. Those subjects who improved most started low, gradually approaching normal levels with experience. Learning effects were more pronounced peripherally than paracentrally and "untrained" fields characteristically showed concentric contraction with numerous points with low sensitivity peripherally. An important practical conclusion is to allow repeated testing of all inexperienced patients in whom initial fields do not agree with clinical findings. A chart showing a concentrically narrowed field should be viewed with particular suspicion. Furthermore, a single initial field may constitute an inadequate baseline for clinical follow-up.
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| 28. |
- Heijl, A, et al.
(författare)
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Visual field interpretation with empiric probability maps
- 1989
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Ingår i: Archives of Ophthalmology. - : American Medical Association (AMA). - 0003-9950. ; 107:2, s. 8-204
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Tidskriftsartikel (refereegranskat)abstract
- Automated visual field charts may be difficult to interpret partly because of the magnitude and complex nature of normal threshold variability. We devised two types of empiric probability maps in which this variability is taken into account and the significances of measured threshold values are displayed. These maps are highly sensitive to nonobvious but significant paracentral field loss but will at the same time deemphasize false-positive patterns commonly found more peripherally. They also frequently show field defects before these are obvious in conventional threshold printouts. In addition, they differentiate between generalized loss of sensitivity and localized field defects.
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| 29. |
- Holmquist, Björn, et al.
(författare)
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Correlation measures for circular data
- 1985
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Ingår i: Contributions to probability and statistics in honour of Gunnar Blom. ; , s. 157-168
-
Bokkapitel (refereegranskat)
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| 30. |
- Holst, Ulla, et al.
(författare)
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Recursive estimation in mixture models with Markov regime
- 1991
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448. ; 37:6, s. 1683-1690
-
Tidskriftsartikel (refereegranskat)abstract
- A recursive algorithm is proposed for estimation of parameters in mixture models, where the observations are governed by a hidden Markov chain. The performance of the algorithm is studied by simulations of a symmetric normal mixture. The algorithm seems to be stable and produce approximately normally distributed estimates, provided the adaptive matrix is kept well conditioned.
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| 31. |
- Holst, Ulla, et al.
(författare)
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Recursive estimation in switching autoregressions with Markov regime
- 1994
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Ingår i: Journal of Time Series Analysis. - : Wiley. - 0143-9782 .- 1467-9892. ; 15:5, s. 489-506
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Tidskriftsartikel (refereegranskat)abstract
- A hidden Markov regime is a Markov process that governs the time or space dependent distributions of an observed stochastic process. We propose a recursive algorithm for parameter estimation in a switching autoregressive process governed by a hidden Markov chain. A common approach to the recursive estimation problem is to base the estimation on suboptimal modifications of Kalman filtering techniques. The main idea in this paper is to use the maximum likelihood method and from this develop a recursive EM algorithm.
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| 32. |
- Hsing, T. L., et al.
(författare)
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Remembering Ross Leadbetter: some personal recollections
- 2023
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Ingår i: Extremes. - 1386-1999 .- 1572-915X. ; In Press
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Ross Leadbetter had had a broad and deep influence on the development of probabilistic and statistical theory of extreme values and on the application of extreme-value methods. He has been an inspiration and a friend for many of us. This editorial collects thirteen personal recollections of Ross and his work. An account of his career and some of his work can be found in the IMS Obituary “Ross Leadbetter 1931–2022”.
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| 33. |
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| 34. |
- Jack, Cuzick, et al.
(författare)
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Frequency estimation from crossings of an unknown level
- 1980
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Ingår i: Biometrika. - : Oxford University Press (OUP). - 0006-3444 .- 1464-3510. ; 67:1, s. 65-72
-
Tidskriftsartikel (refereegranskat)abstract
- By counting the number of upcrossings of the mean level by a stationary Gaussian process one can estimate the mean frequency of the process. Here we present a frequency estimator based on the number of upcrossings of one unknown level hoped to be near the mean, and the percentage of the total observation time spent above the level. This is equivalent to observing upcrossings of a known level in a process with unknown mean and variance. Formulae are given for the bias and variance of the estimator, and conditions for its asymptotic normality. Numerical examples show that the estimator behaves reasonably for levels within one standard deviation from the process mean.
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| 35. |
- Jacobsson, C., et al.
(författare)
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Jet identification based on probability calculations using Bayes' theorem
- 1995
-
Ingår i: Physical Review D (Particles and Fields). - 0556-2821. ; 52:1, s. 162-174
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Tidskriftsartikel (refereegranskat)abstract
- The problem of identifying jets at CERN LEP and DESY HERA is studied. Identification using jet energies and fragmentation properties is treated separately in order to investigate the degree of quark-gluon separation that can be achieved by either of these approaches. In the case of the fragmentation-based identification, a neural network is used, and a test of the dependence on the jet production process and the fragmentation model is done. Instead of working with the separation variables directly, these are used to calculate probabilities of having a specific type of jet, according to Bayes’ theorem. This offers a direct interpretation of the performance of the jet identification and provides a simple means of combining the results of the energy- and fragmentation-based identifications.
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| 36. |
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| 37. |
- Johansson, Mikael, et al.
(författare)
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Memory for perceived and imagined pictures: An event-related potential study
- 2002
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Ingår i: Neuropsychologia. - 1873-3514. ; 40:7, s. 986-1002
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Tidskriftsartikel (refereegranskat)abstract
- Event-related potentials (ERPs) and behavioral measures were used to investigate recognition memory and source-monitoring judgements about previously perceived and imagined pictures. At study, word labels of common objects were presented. Half of these were followed by a corresponding picture and the other half by an empty frame, signalling to the Ss (aged 20-35 yrs) to mentally visualize an image. At test, Ss in a source-monitoring task made a 3-way discrimination between new words and words corresponding to previously perceived and imagined pictures. Ss in an old/new-recognition task indicated whether test words were previously presented or not. In both tasks, correctly identified old items elicited more positive-going ERPs than correctly judged new items. This widely distributed old/new effect was found to have an earlier onset and to be of a greater magnitude for imagined than for perceived items. Task affected the old/new effects over prefrontal areas and the reaction times to remembered old items. Findings are consistent with the view that a greater amount, or a different type, of information is necessary for accurate source-memory judgements than for correct recognition, and moreover, that different types of source-specifying information revive at different rates.
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| 38. |
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| 39. |
- Juston, John, 1960-
(författare)
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Water and Carbon Balance Modeling: Methods of Uncertainty Analysis
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- How do additional data of the same and/or different type contribute to reducing model parameter and predictive uncertainties? This was the question addressed with two models – the HBV hydrological water balance model and the ICBM soil carbon balance model – that were used to investigate the usefulness of the Generalized Likelihood Uncertainty Estimation (GLUE) method for calibrations and uncertainty analyses. The GLUE method is based on threshold screening of Monte Carlo simulations using so-called informal likelihood measures and subjective acceptance criterion. This method is highly appropriate for model calibrations when errors are dominated by epistemic rather than stochastic uncertainties. The informative value of data for model calibrations was investigated with numerous calibrations aimed at conditioning posterior parameter distributions and boundaries on model predictions. The key results demonstrated examples of: 1) redundant information in daily time series of hydrological data; 2) diminishing returns in the value of continued time series data collections of the same type; 3) the potential value of additional data of a different type; 4) a means to effectively incorporate fuzzy information in model calibrations; and 5) the robustness of estimated parameter uncertainty for portability of a soil carbon model between and tropical climate zones. The key to obtaining these insights lied in the methods of uncertainty analysis used to produce them. A paradigm for selecting between formal and informal likelihood measures in uncertainty analysis is presented and discussed for future use within a context of climate related environmental modeling.
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| 40. |
- Kraja, Aldi T., et al.
(författare)
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New Blood Pressure-Associated Loci Identified in Meta-Analyses of 475000 Individuals
- 2017
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Ingår i: Circulation. - : LIPPINCOTT WILLIAMS & WILKINS. - 1942-325X .- 1942-3268. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- Background - Genome-wide association studies have recently identified >400 loci that harbor DNA sequence variants that influence blood pressure (BP). Our earlier studies identified and validated 56 single nucleotide variants (SNVs) associated with BP from meta-analyses of exome chip genotype data. An additional 100 variants yielded suggestive evidence of association.Methods and Results - Here, we augment the sample with 140886 European individuals from the UK Biobank, in whom 77 of the 100 suggestive SNVs were available for association analysis with systolic BP or diastolic BP or pulse pressure. We performed 2 meta-analyses, one in individuals of European, South Asian, African, and Hispanic descent (pan-ancestry, approximate to 475000), and the other in the subset of individuals of European descent (approximate to 423000). Twenty-one SNVs were genome-wide significant (P<5x10(-8) ) for BP, of which 4 are new BP loci: rs9678851 (missense, SLC4A1AP), rs7437940 (AFAP1), rs13303 (missense, STAB1), and rs1055144 (7p15.2). In addition, we identified a potentially independent novel BP-associated SNV, rs3416322 (missense, SYNPO2L) at a known locus, uncorrelated with the previously reported SNVs. Two SNVs are associated with expression levels of nearby genes, and SNVs at 3 loci are associated with other traits. One SNV with a minor allele frequency <0.01, (rs3025380 at DBH) was genome-wide significant.Conclusions - We report 4 novel loci associated with BP regulation, and 1 independent variant at an established BP locus. This analysis highlights several candidate genes with variation that alter protein function or gene expression for potential follow-up.
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| 41. |
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| 42. |
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| 43. |
- Lindgren, Georg
(författare)
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A detailed statistical representation of the local structure of optical vortices in random wavefields
- 2012
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Ingår i: Journal of Optics. - : IOP Publishing. - 2040-8986 .- 2040-8978. ; 14:3
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Tidskriftsartikel (refereegranskat)abstract
- The statistical properties near phase singularities in a complex wave field are here studied by means of the conditional distributions of the real and imaginary Gaussian components, given a common zero crossing point. The exact distribution is expressed as a Slepian model, where a regression term provides the main structure, with parameters given by the gradients of the Gaussian components at the singularity, and Gaussian non-stationary residuals that provide local variability. This technique differs from the linearisation (Taylor expansion) technique commonly used. The empirically and theoretically verified elliptic eccentricity of the intensity contours in the vortex core is a property of the regression term, but with different normalization compared to the classical theory. The residual term models the statistical variability around these ellipses. The radii of the circular contours of the current magnitude are similarly modified by the new regression expansion, and also here the random deviations are modelled by the residual field.
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| 44. |
- Lindgren, Georg A., et al.
(författare)
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Inland subsurface water system role for coastal nitrogen load dynamics and abatement responses
- 2007
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 41:7, s. 2159-2164
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Tidskriftsartikel (refereegranskat)abstract
- We simulate and analyze long-term dynamics of coastalnitrogen (N) loading and the inland source changes andprocesses that may have determined its development overthe past 60-year period and may govern its possiblefuture responses to variousNsource management scenarios.With regard to processes, the results show that averagebasin-scale N delivery fractions to the coast may not berepresentative of the coastal impacts of either diffuse orpoint inland sources. The effects of inland source changesmay be greatly redistributed in space-time and delayedby slow N transport and mass transfer processes in thesubsurface water system of coastal catchments. Extrapolationof current N transport-attenuation conditionsfor quantification of future abatement effects may thereforebe misleading if the extrapolation models do not realisticallyrepresent delayed long-term influences of slow subsurfaceprocesses. With regard to policy, the results show that andwhy national Swedish and international Baltic Searegion policies for coastal N load abatement may bedifficult or impossible to achieve by inland source abatementonly. Large mitigation of both point and diffuse sourcesmay be necessary to achieve targeted coastal N loadreductions fast and maintain them also in the long term.
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| 45. |
- Lindgren, Georg
(författare)
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A note on the asymptotic independence of high level crossings for dependent Gaussian processes
- 1974
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Ingår i: Annals of Probability. - : Institute of Mathematical Statistics. - 0091-1798. ; 2:3, s. 535-539
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that the numbers of high level crossings by p dependent stationary Gaussian processes have asymptotically independent Poisson distributions if the observation interval and the height of the level increase in a coordinated way. The processes may be highly correlated, even linearly dependent.
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| 46. |
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| 47. |
- Lindgren, Georg
(författare)
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Asymmetric waves in wave energy systems analysed by the stochastic Gauss-Lagrange wave model
- 2015
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Ingår i: Proceedings of the Estonian Academy of Sciences. - : Estonian Academy Publishers. - 1736-7530 .- 1736-6046. ; 64:3, s. 291-296
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Tidskriftsartikel (refereegranskat)abstract
- The Gauss-Lagrange stochastic wave model is known to produce irregular waves with realistic degrees of asymmetry. We present the basic structure of the model and illustrate three of its characteristic properties: front-back asymmetry, particle orbits, and average horseshoe pattern. We also study the effect of a linear filter in a wave energy converting (WEC) system on asymmetry and on average power of the system.
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| 48. |
- Lindgren, Georg, et al.
(författare)
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Bertil Matérn
- 2018
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Ingår i: Wiley StatsRef : Statistics Reference Online - Statistics Reference Online. - : Wiley.
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Bokkapitel (refereegranskat)abstract
- Bertil Matérn (1917–2007) was a Swedish forester and mathematical statistician. His most important contribution was his dissertation Spatial Variation, which contains much of the mathematical foundation of spatial statistics.
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| 49. |
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| 50. |
- Lindgren, Georg, et al.
(författare)
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Charlier, Carl V.L.
- 2018
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Ingår i: Wiley StatsRef : Statistics Reference Online - Statistics Reference Online. - : Wiley.
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Bokkapitel (refereegranskat)abstract
- Carl Charlier was a Swedish astronomer and statistician. He was influential in making mathematical statistics a university subject in Sweden. His main statistical contribution was the Gram‐Charlier expansions of continuous (Type A) and discrete (Type B) distributions. In astronomy he successfully created a hierarchical galaxy cluster model.
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