1,723,654 research outputs found
Long-term follow-up of 140 children with hepatoblastoma after CR in Beijing Tongren hospital, Beijing, China
No full textLong-term follow-up of 140 children with hepatoblastoma after CR in Beijing Tongren hospital, Beijing, Chin
Topics and Applications of Weighting Methods in Case-Control and Observational Studies
No full textWeighting methods have been widely used in statistics and related applications. For example, the inverse probability weighting is a standard approach to correct for survey non-response. The case-control design, frequently seen in epidemiologic or genetic studies, can be regarded as a special type of survey design; analogous inverse probability weighting approaches have been explored when the interest is the association between exposures and the disease (primary analysis) as well as when the interest is the association among exposures (secondary analysis). Meanwhile, in observational comparative effectiveness research, inverse probability weighting has been suggested as a valid approach to correct for confounding bias. This dissertation develops and extends weighting methods for case-control and observational studies.The first part of this dissertation extends the inverse probability weighting approach for secondary analysis of case-control data. We revisit an inverse probability weighting estimator to offer new insights and extensions. Specifically, we construct its more general form by generalized least squares (GLS). Such a construction allows us to connect the GLS estimator with the generalized method of moments and motivates a new specification test designed to assess the adequacy of the inverse probability weights. The specification test statistic measures the weighted discrepancy between the case and control subsample estimators, and asymptotically follows a Chi-squared distribution under correct model specification. We illustrate the GLS estimator and specification test using a case-control sample of peripheral arterial disease, and use simulations to shed light on the operating characteristics of the specification test. The second part develops a robust difference-in-differences (DID) estimator for estimating causal effect with observational before-after data. Within the DID framework, two common estimation strategies are outcome regression and propensity score weighting. Motivated by a real application in traffic safety research, we propose a new double-robust DID estimator that hybridizes outcome regression and propensity score weighting. We show that the proposed estimator possesses the desirable large-sample robustness property, namely the consistency only requires either one of the outcome model or the propensity score model to be correctly specified. We illustrate the new estimator to study the causal effect of rumble strips in reducing vehicle crashes, and conduct a simulation study to examine its finite-sample performance. The third part discusses a unified framework, the balancing weights, for estimating causal effects in observational studies with multiple treatments. These weights incorporate the generalized propensity scores to balance the weighted covariate distribution of each treatment group, all weighted toward a common pre-specified target population. Within this framework, we further develop the generalized overlap weights, constructed as the product of the inverse probability weights and the harmonic mean of the generalized propensity scores. The generalized overlap weights corresponds to the target population with the most overlap in covariates between treatments, similar to the population in equipoise in clinical trials. We show that the generalized overlap weights minimize the total asymptotic variance of the nonparametric estimators for the pairwise contrasts within the class of balancing weights. We apply the new weighting method to study the racial disparities in medical expenditure and further examine its operating characteristics by simulations.</p
Recommended from our members
Author Correction: An NF-κB-microRNA regulatory network tunes macrophage inflammatory responses.
Full text linkLi-Fan Lu and Alexander Y. Rudensky, who supplied miR-146a floxed mice used in this study, were inadvertently omitted from the author list in the originally published version of this Article. This has now been corrected in both the PDF and HTML versions of the Article. The generation of the floxed mice has been described in detail by Cho and Lee et al.1
Pegomya tenuiramula Ge, Li & Fan 1988
No full texttenuiramula Ge, Li & Fan in Fan et al., 1988b: 338 (Pegomya). Holotype male with labels: (1) printed with handwritten inscriptions on white label: “ Gansu Diebu / Chinese Academy of Sciences ”; (2) printed with handwritten inscriptions on white label: “19 79.IV.17 / collector Jianyi Wu and Xinmin Li”; (3) handwritten on white label: “ Pegomya tenuiramula ”; (4) printed with handwritten inscriptions on red label: “ TYPE / Pegomya / tenuiramula / Ge, Li et Fan ”. Preservation: pinned. Missing parts: left hind leg and all right legs. Paratype male with labels: (1) printed with handwritten inscriptions on white label: “ Gansu Diebu / Chinese Academy of Sciences ”; (2) printed with handwritten inscriptions on white label: “19 79.IV.17 / collector Jianyi Wu and Xinmin Li”; (3) handwritten on white label: “ Pegomya / tenuiramula / sp.n.”; (4) printed with handwritten inscriptions on red label: “ PARATYPE / Pegomya / tenuiramula / Ge, Li et Fan ”. Preservation: pinned; genitalia dissected and mounted on paper triangle, left wing and legs mounted on paper triangle. Current name: Pegomya tenuiramula Ge, Li & Fan, 1988.Published as part of ZHANG, XUFENG & ZHU, WEIBING, 2014, The types of Anthomyiidae (Diptera) in the Shanghai Entomological Museum, Chinese Academy of Science, China, pp. 1-67 in Zootaxa 3756 (1) on page 55, DOI: 10.11646/zootaxa.3756.1.1, http://zenodo.org/record/503313
Pegohylemyia macrospinigera Deng, Li & Fan 1990
No full textmacrospinigera Deng, Li & Fan, 1990: 247 (Pegohylemyia). Holotype male with labels: (1) printed on white label: “Jinding / 82.7”; (2) printed with handwritten inscriptions on white label: “ Pegohylemyia / macrospinigera / Identifier: Zide Fan ”; (3) a red label with no writing; (4) printed with handwritten inscriptions on red label: “ TYPE / Botanophila / macrospinigera / (Deng, Li et Fan) ”. Preservation: pinned; genitalia dissected and mounted on slide pinned with the specimen. Missing parts: mid legs and hind leg. Paratype male with labels: (1) printed on white label: “Leidongping / 82.6”; (2) printed on yellow label: “ PARATYPE ”; (3) printed with handwritten inscriptions on white label: “ Pegohylemyia / macrospinigera / Identifier: Zide Fan ”; (4) printed with handwritten inscriptions on red label: “ PARATYPE / Botanophila / macrospinigera / (Deng, Li et Fan) ”. Preservation: pinned. Missing parts: right wing; left legs. Current name: Botanophila macrospinigera (Deng, Li & Fan, 1990).Published as part of ZHANG, XUFENG & ZHU, WEIBING, 2014, The types of Anthomyiidae (Diptera) in the Shanghai Entomological Museum, Chinese Academy of Science, China, pp. 1-67 in Zootaxa 3756 (1) on pages 35-36, DOI: 10.11646/zootaxa.3756.1.1, http://zenodo.org/record/503313
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Do Debit Cards Decrease Cash Demand?: Causal Inference and Sensitivity Analysis Using Principal Stratification
No full textIt has been argued that the use of debit cards may modify the cash holding behaviour, as debit card holders may either withdraw cash from ATMs (Automated Teller Machine) or purchase items using POS (Point of Sale) devices at retailers. In this paper, within the Rubin Causal Model, we investigate the causal effects of the use of debit cards on the cash inventories held by households using data from the Italy Survey of Household Income and Wealth. We adopt the principal stratification approach to incorporate the share of debit card holders who do not use this payment instrument. We use a regression model with the propensity score as the single predictor to adjust for the imbalance in observed covariates. We further develop a sensitivity analysis approach to assess the sensitivity of the proposed model to violation to the key unconfoundedness assumption. Our empirical results suggest statistically significant negative effects of debit cards on the household cash level in Italy
FIGURE 10 in Rhodeus albomarginatus, a new bitterling (Te le os te i: Cyprinidae: Acheilognathinae) from China
No full textFIGURE 10. Habitat of Rhodeus albomarginatus, China: Anhui Province: Qimen County.Published as part of Li, Fan & Arai, Ryoichi, 2014, Rhodeus albomarginatus, a new bitterling (Te le os te i: Cyprinidae: Acheilognathinae) from China, pp. 165-176 in Zootaxa 3790 (1) on page 173, DOI: 10.11646/zootaxa.3790.1.7, http://zenodo.org/record/25092
- …
