| 1. |
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| 2. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 3. |
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| 4. |
- Kanai, M, et al.
(författare)
-
- 2023
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swepub:Mat__t
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| 5. |
- Grüning, Björn, et al.
(författare)
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Bioconda: A sustainable and comprehensive software distribution for the life sciences
- 2017
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present Bioconda (https://bioconda.github.io), a distribution of bioinformatics software for the lightweight, multi-platform and language-agnostic package manager Conda. Currently, Bioconda offers a collection of over 3000 software packages, which is continuously maintained, updated, and extended by a growing global community of more than 200 contributors. Bioconda improves analysis reproducibility by allowing users to define isolated environments with defined software versions, all of which are easily installed and managed without administrative privileges.
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| 6. |
- Hudson, Lawrence N, et al.
(författare)
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The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project
- 2017
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Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 7:1, s. 145-188
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Tidskriftsartikel (refereegranskat)abstract
- The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.
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| 7. |
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| 8. |
- Birney, Ewan, et al.
(författare)
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Identification and analysis of functional elements in 1% of the human genome by the ENCODE pilot project
- 2007
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 447:7146, s. 799-816
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Tidskriftsartikel (refereegranskat)abstract
- We report the generation and analysis of functional data from multiple, diverse experiments performed on a targeted 1% of the human genome as part of the pilot phase of the ENCODE Project. These data have been further integrated and augmented by a number of evolutionary and computational analyses. Together, our results advance the collective knowledge about human genome function in several major areas. First, our studies provide convincing evidence that the genome is pervasively transcribed, such that the majority of its bases can be found in primary transcripts, including non-protein-coding transcripts, and those that extensively overlap one another. Second, systematic examination of transcriptional regulation has yielded new understanding about transcription start sites, including their relationship to specific regulatory sequences and features of chromatin accessibility and histone modification. Third, a more sophisticated view of chromatin structure has emerged, including its inter-relationship with DNA replication and transcriptional regulation. Finally, integration of these new sources of information, in particular with respect to mammalian evolution based on inter- and intra-species sequence comparisons, has yielded new mechanistic and evolutionary insights concerning the functional landscape of the human genome. Together, these studies are defining a path for pursuit of a more comprehensive characterization of human genome function.
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| 9. |
- Baranowska-Rataj, Anna, 1980-, et al.
(författare)
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Does the number of siblings affect health in midlife? : Evidence from the Swedish Prescribed Drug Register
- 2016
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Ingår i: Demographic Research. - Max Planck Institute for Demographic Research. - 1435-9871. ; 35, s. 1259-1302
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Tidskriftsartikel (refereegranskat)abstract
- Background: In many societies, growing up in a large family is associated with receiving less parental time, attention, and financial support. As a result, children with a large number of siblings may have worse physical and mental health outcomes than children with fewer siblings.Objective: Our objective is to examine the long-term causal effects of sibship size on physical and mental health in modern Sweden.Methods: We employ longitudinal data covering the entire Swedish population from the Multigenerational Register and the Medical Birth Register. This data includes information on family size and on potential confounders such as parental background. We use the Prescribed Drug Register to identify the medicines that have been prescribed and dispensed. We use instrumental variable models with multiple births as instruments to examine the causal effects of family size on the health outcomes of children, as measured by receiving medicines at age 45.Results: Our results indicate that in Sweden, growing up in a large family does not have a detrimental effect on physical and mental health in midlife.Contribution: We provide a systematic overview of the health-related implications of growing up in a large family. We adopt a research design that gives us the opportunity to make causal inferences about the long-term effects of family size. Moreover, our paper provides evidence on the links between family size and health outcomes in the context of a developed country that implements policies oriented towards reducing social inequalities in health and other living conditions.
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| 10. |
- Barban, Nicola, et al.
(författare)
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Causal Effects of the Timing of Life-course Events : Age at Retirement and Subsequent Health
- 2020
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Ingår i: Sociological Methods & Research. - : Sage Publications. - 0049-1241 .- 1552-8294. ; 49:1, s. 216-249
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we combine the extensive literature on the analysis of life-course trajectories as sequences with the literature on causal inference and propose a new matching approach to investigate the causal effect of the timing of life-course events on subsequent outcomes. Our matching approach takes into account pre-event confounders that are both time-independent and time-dependent as well as life-course trajectories. After matching, treated and control individuals can be compared using standard statistical tests or regression models. We apply our approach to the study of the consequences of the age at retirement on subsequent health outcomes, using a unique data set from Swedish administrative registers. Once selectivity in the timing of retirement is taken into account, effects on hospitalization are small, while early retirement has negative effects on survival. Our approach also allows for heterogeneous treatment effects. We show that the effects of early retirement differ according to preretirement income, with higher income individuals tending to benefit from early retirement, while the opposite is true for individuals with lower income.
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| 11. |
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| 12. |
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Bayes de Luna, Antonio, et al.
(författare)
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Interatrial blocks. A separate entity from left atrial enlargement: a consensus report
- 2012
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 45:5, s. 445-451
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Tidskriftsartikel (refereegranskat)abstract
- Impaired interatrial conduction or interatrial block is well documented but is not described as an individual electrocardiographic (ECG) pattern in most of ECG books, although the term atrial abnormalities to encompass both concepts, left atrial enlargement (LAE) and interatrial block, has been coined. In fact, LAE and interatrial block are often associated, similarly to what happens with ventricular enlargement and ventricular block. The interatrial blocks, that is, the presence of delay of conduction between the right and left atria, are the most frequent atrial blocks. These may be of first degree (P-wave duration > 120 milliseconds), third degree (longer P wave with biphasic [+/-] morphology in inferior leads), and second degree when these patterns appear transiently in the same ECG recording (atrial aberrancy). There are evidences that these electrocardiographic P-wave patterns are due to a block because they may (a) appear transiently, (b) be without associated atrial enlargement, and (c) may be reproduced experimentally. The presence of interatrial blocks may be seen in the absence of atrial enlargement but often are present in case of LAE. The most important clinical implications of interatrial block are the following: (a) the first degree interatrial blocks are very common, and their relation with atrial fibrillation and an increased risk for global and cardiovascular mortality has been demonstrated; (b) the third degree interatrial blocks are less frequent but are strong markers of LAE and paroxysmal supraventricular tachyarrhythmias. Their presence has been considered a true arrhythmological syndrome. (C) 2012 Elsevier Inc. All rights reserved.
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| 17. |
- Broström, Göran, et al.
(författare)
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Att läsa i Umeå är ett bra val
- 2005
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Ingår i: Västerbottens-Kuriren. ; :9 december, s. 4-
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 18. |
- Bränberg, Kenny, 1956-
(författare)
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Observed score equating with covariates
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In test score equating the focus is on the problem of finding the relationship between the scales of different test forms. This can be done only if data are collected in such a way that the effect of differences in ability between groups taking different test forms can be separated from the effect of differences in test form difficulty. In standard equating procedures this problem has been solved by using common examinees or common items. With common examinees, as in the equivalent groups design, the single group design, and the counterbalanced design, the examinees taking the test forms are either exactly the same, i.e., each examinee takes both test forms, or random samples from the same population. Common items (anchor items) are usually used when the samples taking the different test forms are assumed to come from different populations. The thesis consists of four papers and the main theme in three of these papers is the use of covariates, i.e., background variables correlated with the test scores, in observed score equating. We show how covariates can be used to adjust for systematic differences between samples in a non-equivalent groups design when there are no anchor items. We also show how covariates can be used to decrease the equating error in an equivalent groups design or in a non-equivalent groups design. The first paper, Paper I, is the only paper where the focus is on something else than the incorporation of covariates in equating. The paper is an introduction to test score equating, and the author's thoughts on the foundation of test score equating. There are a number of different definitions of test score equating in the literature. Some of these definitions are presented and the similarities and differences between them are discussed. An attempt is also made to clarify the connection between the definitions and the most commonly used equating functions. In Paper II a model is proposed for observed score linear equating with background variables. The idea presented in the paper is to adjust for systematic differences in ability between groups in a non-equivalent groups design by using information from background variables correlated with the observed test scores. It is assumed that conditional on the background variables the two samples can be seen as random samples from the same population. The background variables are used to explain the systematic differences in ability between the populations. The proposed model consists of a linear regression model connecting the observed scores with the background variables and a linear equating function connecting observed scores on one test forms to observed scores on the other test form. Maximum likelihood estimators of the model parameters are derived, using an assumption of normally distributed test scores, and data from two administrations of the Swedish Scholastic Assessment Test are used to illustrate the use of the model. In Paper III we use the model presented in Paper II with two different data collection designs: the non-equivalent groups design (with and without anchor items) and the equivalent groups design. Simulated data are used to examine the effect - in terms of bias, variance and mean squared error - on the estimators, of including covariates. With the equivalent groups design the results show that using covariates can increase the accuracy of the equating. With the non-equivalent groups design the results show that using an anchor test together with covariates is the most efficient way of reducing the mean squared error of the estimators. Furthermore, with no anchor test, the background variables can be used to adjust for the systematic differences between the populations and produce unbiased estimators of the equating relationship, provided that the “right” variables are used, i.e., the variables explaining those differences. In Paper IV we explore the idea of using covariates as a substitute for an anchor test with a non-equivalent groups design in the framework of Kernel Equating. Kernel Equating can be seen as a method including five different steps: presmoothing, estimation of score probabilities, continuization, equating, and calculating the standard error of equating. For each of these steps we give the theoretical results when observations on covariates are used as a substitute for scores on an anchor test. It is shown that we can use the method developed for Post-Stratification Equating in the non-equivalent groups with anchor test design, but with observations on the covariates instead of scores on an anchor test. The method is illustrated using data from the Swedish Scholastic Assessment Test.
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| 19. |
- Brännäs, Kurt, et al.
(författare)
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Generalized method of moment and indirect estimation of the ARasMA model
- 1998
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Ingår i: Computational statistics (Zeitschrift). - 0943-4062 .- 1613-9658. ; 13:4, s. 485-494
-
Tidskriftsartikel (refereegranskat)abstract
- Estimation in nonlinear time series models has mainly been performed by least squares or maximum likelihood (ML) methods. The paper suggests and studies the performance of generalized method of moments (GMM) and indirect estimators for the autoregressive asymmetric moving average model. Both approaches are easy to implement and perform well numerically. In a Monte Carlo study it is found that the MSE properties of GMM are close to those of ML. The indirect estimator performs poorly in this respect. On the other hand, the three estimation techniques lead to fairly similar power functions for a linearity test.
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| 20. |
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| 21. |
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| 22. |
- Cantoni, Eva, et al.
(författare)
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Semiparametric inference with missing data : robustness to outliers and model misspecification
- 2020
-
Ingår i: Econometrics and Statistics. - : Elsevier. - 2452-3062. ; 16, s. 108-120
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Tidskriftsartikel (refereegranskat)abstract
- Classical semiparametric inference with missing outcome data is not robust to contamination of the observed data and a single observation can have arbitrarily large influence on estimation of a parameter of interest. This sensitivity is exacerbated when inverse probability weighting methods are used, which may overweight contaminated observations. Inverse probability weighted, double robust and outcome regression estimators of location and scale parameters are introduced, which are robust to contamination in the sense that their influence function is bounded. Asymptotic properties are deduced and finite sample behaviour studied. Simulated experiments show that contamination can be more serious a threat to the quality of inference than model misspecification. An interesting aspect of the results is that the auxiliary outcome model used to adjust for ignorable missingness by some of the estimators, is also useful to protect against contamination. Both adjustment to ignorable missingness and protection against contamination are achieved through weighting schemes. A case study illustrates how the resulting weights can be studied to gain insights on how the two different weighting schemes interact.
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| 23. |
- Chaparro, M. Pia, et al.
(författare)
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Childhood family structure and women's adult overweight risk : A longitudinal study
- 2017
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Ingår i: Scandinavian Journal of Public Health. - : SAGE Publications. - 1403-4948 .- 1651-1905. ; 45:5, s. 511-519
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Tidskriftsartikel (refereegranskat)abstract
- AIM: The aim of this study was to investigate whether women's adult overweight and obesity risk was associated with their childhood family structure, measured as their mothers' marital status history, during the women's first 18 years of life.METHODS: Using linked register data, we analyzed 30,584 primiparous women born in Sweden in 1975 who were between 19-35 years of age when their height and pre-pregnancy weight was recorded. The outcomes were women's overweight/obesity (body mass index (BMI) ≥ 25 kg/m(2)) and obesity (BMI ≥ 30 kg/m(2)) and the predictor was mothers' marital status history, which was summarized using sequence analysis. We carried out nested logistic regression models adjusting for women's age and maternal sociodemographic characteristics.RESULTS: Mothers' marital status history was summarized into six clusters: stable marriage, stable cohabitation, married then divorcing, cohabiting then separating, varied transitions, and not with father. In fully adjusted models and compared with women whose mothers belonged to the stable marriage cluster: (1) women whose mothers belonged to the other marital status clusters had higher odds of overweight/obesity (odds ratio (OR) ranging 1.15-1.19; p < 0.05); and (2) women whose mothers belonged to the stable cohabitation (OR = 1.31; 95% confidence interval (CI) = 1.14-1.52), cohabiting then separating (OR = 1.23; 95% CI = 1.01-1.49), varied transitions (OR = 1.24; 95% CI = 1.11-1.39), and not with father (OR = 1.24; 95% CI = 1.00-1.54) clusters had higher odds of obesity.CONCLUSIONS: Women whose mothers were not in stable marriage relationships had higher odds of being overweight or obese in adulthood. The finding that even women raised in the context of stable cohabitation had higher odds of being overweight or obese is intriguing as these relationships are socially accepted in Sweden.
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| 24. |
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| 25. |
- Chaparro, Pia, et al.
(författare)
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Regional inequalities in pre-pregnancy overweight and obesity in Sweden, 1992, 2000, and 2010
- 2015
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Ingår i: Scandinavian Journal of Public Health. - : SAGE Publications. - 1403-4948 .- 1651-1905. ; 43:5, s. 534-539
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Tidskriftsartikel (refereegranskat)abstract
- Aims: To investigate regional differences and time trends in women's overweight and obesity in Sweden. Methods: Using data from the Swedish Medical Birth Register (women aged 18 years, first pregnancy only) and the Total Population Register accessed through the Umea SIMSAM Lab, age-standardized prevalence of pre-pregnancy overweight/obesity (BMI 25 kg/m(2)) and obesity (BMI 30 kg/m(2)) were estimated by county for the years 1992, 2000, and 2010. Maps were created using ArcMap v10.2.2 to display regional variations over time and logistic regression analyses were used to assess if the observed trends were significant. Results: The prevalence of pre-pregnancy overweight/obesity and obesity increased significantly in all Swedish counties between 1992, and 2010. In 2010, Sodermanland and Gotland exhibited the highest age-standardized overweight/obesity (39.7%) and obesity (15.1%) prevalence, respectively. The sharpest increases between 1992 and 2010 were observed in Vasterbotten for overweight/obesity (75% increase) and in Gotland for obesity (233% increase). Across the years, Stockholm had the lowest prevalence of overweight/obesity (26.3% in 2010) and obesity (7.3% in 2010) and one of the least steep increases in prevalence of both between 1992 and 2010. Conclusions: Substantial regional differences in pre-pregnancy overweight and obesity prevalence are apparent in Sweden. Further research should elucidate the mechanisms causing these differences.
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| 26. |
- Daunfeldt, Sven-Olov, et al.
(författare)
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Central bank independence and price stability : evidence from OECD-countries
- 2008
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Ingår i: Oxford Economic Papers. - Oxford : Oxford University Press (OUP). - 0030-7653 .- 1464-3812. ; 60:3, s. 410-422
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we use a non-parametric regression method to compare the transition process from high to low inflation with the implementation dates of central bank independence reforms. In most countries, price stability is achieved before more independence is given to the central bank. Moreover, for those countries which have implemented a central bank independence reform under a high inflation regime, no evidence is found that the reforms have actually led to price stability. This suggests that the credibility of a low inflation goal can be achieved without institutional reforms which grant the central bank more independence from the political policymakers.
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| 27. |
- Daunfeldt, Sven-Olov, et al.
(författare)
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Efficacy and Cost of Regime Shifts in Inflation Policies : Evidence from New Zealand and Sweden
- 2001
-
Ingår i: Applied Economics. - 0003-6846 .- 1466-4283. ; 33:2, s. 217-224
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper a comparative study of the regime shift in inflation policies in New Zealand and Sweden is performed. A nonparametric regression method is used to decompose the inflation time series into three components of variation: a long-term trend, a medium-term (cyclical and transient variations) trend and a short-term shocks component. This allows study of the transition process from the high inflation characterizing the end of the 1970s and the 1980s to the low inflation observed during the 1990s. It is found that in New Zealand, although it is initially delayed, the decrease in inflation happens at a faster pace than in Sweden. This may indicate that reforms were more efficient in New Zealand. A clear link is also shown between the rising unemployment and the transition from high to low inflation. Furthermore, while in New Zealand a downward adjustment of the unemployment rate happens directly after the transition period, in Sweden there seems to be persistence in high unemployment.
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| 28. |
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| 29. |
- de Luna, Xavier, 1968-, et al.
(författare)
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Can adult education delay retirement from the Labour Market?
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Several studies have suggested that education is associated with later retirement from the labour market. In this paper, we examine whether adult education, involving enrolees aged 42 or above, delays retirement to potentially increase labour force participation among the elderly. With Swedish register data of transcripts from adult education and an-nual earnings, which encompasses 1979-2004 and 1982-2004 respectively, we exploit the fact that adult education is a large-scale phenomenon in Sweden and construct a measure of the timing of the transition from being self-supported by productive work to being supported by pension transfers. We match samples of treated and controls on the propen-sity score and use non-parametric estimation of survival rates. The results indicate that adult education has no effect on the timing of the retirement from the labour force. This can be contrasted with the fact that adult education is one of the cornerstones of the OECD strategy for “active ageing” and the European Union’s “Lisbon strategy” for growth and jobs.
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| 30. |
- de Luna, Xavier, et al.
(författare)
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Choosing a Model Selection Strategy
- 2003
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Ingår i: Scandinavian Journal of Statistics. ; 30, s. 113-128
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Tidskriftsartikel (refereegranskat)
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- de Luna, Xavier, et al.
(författare)
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Covariate selection for the non-parametric estimation of an average treatment effect
- 2011
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Ingår i: Biometrika. - : Oxford University Press. - 0006-3444 .- 1464-3510. ; 98:4, s. 861-875
-
Tidskriftsartikel (refereegranskat)abstract
- Observational studies in which the effect of a nonrandomized treatment on an outcome of interest is estimated are common in domains such as labour economics and epidemiology. Such studies often rely on an assumption of unconfounded treatment when controlling for a given set of observed pre-treatment covariates. The choice of covariates to control in order to guarantee unconfoundedness should primarily be based on subject matter theories, although the latter typically give only partial guidance. It is tempting to include many covariates in the controlling set to try to make the assumption of an unconfounded treatment realistic. Including unnecessary covariates is suboptimal when the effect of a binary treatment is estimated nonparametrically. For instance, when using a n1/2-consistent estimator, a loss of efficiency may result from using covariates that are irrelevant for the unconfoundedness assumption. Moreover, bias may dominate the variance when many covariates are used. Embracing the Neyman–Rubin model typically used in conjunction with nonparametric estimators of treatment effects, we characterize subsets from the original reservoir of covariates that are minimal in the sense that the treatment ceases to be unconfounded given any proper subset of these minimal sets. These subsets of covariates are shown to be identified under mild assumptions. These results lead us to propose data-driven algorithms for the selection of minimal sets of covariates.
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| 35. |
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| 36. |
- de Luna, Xavier, et al.
(författare)
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Exogeneity in structural equation models
- 2006
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Ingår i: Journal of Econometrics. - : Elsevier BV. - 0304-4076. ; 132:2, s. 527-543
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Tidskriftsartikel (refereegranskat)abstract
- The practical relevance of several concepts of exogeneity of treatments for the estimation of causal parameters based on observational data are discussed. We show that the traditional concepts, such as strong ignorability and weak and super-exogeneity, are too restrictive if interest lies in average effects (i.e. not on distributional effects of the treatment). We suggest a new definition of exogeneity, KL-exogeneity. It does not rely on distributional assumptions and is not based on counterfactual random variables. As a consequence it can be empirically tested using a proposed test that is simple to implement and is distribution-free.
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| 37. |
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| 38. |
- de Luna, Xavier, et al.
(författare)
-
Graphical diagnostics of endogeneity
- 2008
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Ingår i: Modelling and Evaluating Treatment Effects in Econometrics. - : Emerald Group Publishing Limited. - 9780762313808 - 9781849505239 ; , s. 147-166
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- We show that in sorting cross-sectional data, the endogeneity of a variable may be successfully detected by graphically examining the cumulative sum of the recursive residuals. Moreover, the sign of the bias implied by the endogeneity may be deducible through such graphs. In general, instrumental variables are needed to implement the graphical test. However, when a continuous or ordered (e.g. years of schooling) variable is suspected to be endogenous, a graphical test for misspecification due to endogeneity (e.g. self-selection) can be obtained without instrumental variables.
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| 39. |
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| 40. |
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| 41. |
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| 42. |
- de Luna, Xavier, 1968-, et al.
(författare)
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Non-parametric inference for the effect of a treatment on survival times with application in the health and social sciences
- 2010
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Ingår i: Journal of Statistical Planning and Inference. - : Elsevier. - 0378-3758 .- 1873-1171. ; 140:7, s. 2122-2137
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we perform inference on the effect of a treatment on survival times in studies where the treatment assignment is not randomized and the assignment time is not known in advance. Two such studies are discussed: a heart transplant program and a study of Swedish unemployed eligible for employment subsidy. We estimate survival functions on a treated and a control group which are made comparable through matching on observed covariates. The inference is performed by conditioning on waiting time to treatment, that is, time between the entrance in the study and treatment. This can be done only when sufficient data are available. In other cases, averaging over waiting times is a possibility, although the classical interpretation of the estimated survival functions is lost unless hazards are not functions of waiting time. To show unbiasedness and to obtain an estimator of the variance, we build on the potential outcome framework, which was introduced by J. Neyman in the context of randomized experiments, and adapted to observational studies by D.B. Rubin. Our approach does not make parametric or distributional assumptions. In particular, we do not assume proportionality of the hazards compared. Small sample performance of the estimator and a derived test of no treatment effect are studied in a Monte Carlo study.
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| 43. |
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| 44. |
- de Luna, Xavier, et al.
(författare)
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Proxy variables and nonparametric identification of causal effects
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Proxy variables are often used in linear regression models with the aim of removing potential confounding bias. In this paper we formalise proxy variables within the potential outcome framework, giving conditions under which it can be shown that causal effects are nonparametrically identified. We characterise two types of proxy variables and give concrete examples where the proxy conditions introduced may hold by design.
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| 45. |
- de Luna, Xavier, et al.
(författare)
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Proxy variables and nonparametric identification of causal effects
- 2017
-
Ingår i: Economics Letters. - : Elsevier BV. - 0165-1765 .- 1873-7374. ; 150, s. 152-154
-
Tidskriftsartikel (refereegranskat)abstract
- Proxy variables are often used in linear regression models with the aim of removing potential confounding bias. In this paper we formalise proxy variables within the potential outcomes framework, giving conditions under which it can be shown that causal effects are nonparametrically identified. We characterise two types of proxy variables and give concrete examples where the proxy conditions introduced may hold by design.
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| 46. |
- de Luna, Xavier, et al.
(författare)
-
Robust Simulation-Based Estimation of ARMA Models
- 2001
-
Ingår i: Journal of Computational and Graphical Statistics. ; 10, s. 370-387
-
Tidskriftsartikel (refereegranskat)abstract
- This article proposes a new approach to the robust estimation of a mixed autoregressive and moving average (ARMA) model. It is based on the indirect inference method that originally was proposed for models with an intractable likelihood function. The estimation algorithm proposed is based on an auxiliary autoregressive representation whose parameters are first estimated on the observed time series and then on data simulated from the ARMA model. To simulate data the parameters of the ARMA model have to be set. By varying these we can minimize a distance between the simulation-based and the observation-based auxiliary estimate. The argument of the minimum yields then an estimator for the parameterization of the ARMA model. This simulation-based estimation procedure inherits the properties of the auxiliary model estimator. For instance, robustness is achieved with GM estimators. An essential feature of the introduced estimator, compared to existing robust estimators for ARMA models, is its theoretical tractability that allows us to show consistency and asymptotic normality. Moreover, it is possible to characterize the influence function and the breakdown point of the estimator. In a small sample Monte Carlo study it is found that the new estimator performs fairly well when compared with existing procedures. Furthermore, with two real examples, we also compare the proposed inferential method with two different approaches based on outliers detection.
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| 47. |
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| 48. |
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- de Luna, Xavier, 1968-, et al.
(författare)
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Testing for the Unconfoundedness Assumption Using an Instrumental Assumption
- 2014
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Ingår i: Journal of Causal Inference. - : Walter de Gruyter GmbH. - 2193-3677 .- 2193-3685. ; 2:2, s. 187-199
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Tidskriftsartikel (refereegranskat)abstract
- The identification of average causal effects of a treatment in observational studies is typically based either on the unconfoundedness assumption (exogeneity of the treatment) or on the availability of an instrument. When available, instruments may also be used to test for the unconfoundedness assumption. In this paper, we present a set of assumptions on an instrumental variable which allows us to test for the unconfoundedness assumption, although they do not necessarily yield nonparametric identification of an average causal effect. We propose a test for the unconfoundedness assumption based on the instrumental assumptions introduced and give conditions under which the test has power. We perform a simulation study and apply the results to a case study where the interest lies in evaluating the effect of job practice on employment.
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