Clinical Epidemiology Commons^™

Methodological Issues In The Study Of The Effects Of Hemoglobin Variability, Marshall Joffe, Wei Yang, Steve Brunelli, Harold Feldman

UPenn Biostatistics Working Papers

We consider estimating the effect of hemoglobin variability on mortality in hemodialysis patients. Causal effects can be defined as comparisons of outcomes under different hypothetical interventions. Defining measures of the effect of hemoglobin variability and clinical outcomes is complicated by the fact that hypothetical interventions on variability used to define its effect inevitably involve manipulation of related variables. We propose a model-based definition of the effect of the hemoglobin variability as a parameter for variability in a causal model for the effect of an overall intervention on hemoglobin levels over time. We consider this problem using history-adjusted marginal structural models, …

Adjusting For Covariates In Studies Of Diagnostic, Screening, Or Prognostic Markers: An Old Concept In A New Setting, Holly Janes, Margaret Pepe

UW Biostatistics Working Paper Series

The concept of covariate adjustment is well established in therapeutic and etiologic studies. However, it has received little attention in the growing area of medical research devoted to the development of markers for disease diagnosis, screening, or prognosis, where classification accuracy, rather than association, is of primary interest. In this paper, we demonstrate the need for covariate adjustment in studies of classification accuracy, discuss methods for adjusting for covariates, and distinguish covariate adjustment from several other related but fundamentally different uses for covariates. We draw analogies and contrasts throughout with studies of association.

Assessing The Unreliability Of The Medical Literature: A Response To "Why Most Published Research Findings Are False", Steven Goodman, Sander Greenland

Johns Hopkins University, Dept. of Biostatistics Working Papers

A recent article in this journal (Ioannidis JP (2005) Why most published research findings are false. PLoS Med 2: e124) argued that more than half of published research findings in the medical literature are false. In this commentary, we examine the structure of that argument, and show that it has three basic components:

1)An assumption that the prior probability of most hypotheses explored in medical research is below 50%.

2)Dichotomization of P-values at the 0.05 level and introduction of a “bias” factor (produced by significance-seeking), the combination of which severely weakens the evidence provided by every design.

3)Use of Bayes …

A Cohort Study Of Reproductive And Hormonal Factors And Renal Cell Cancer Risk In Women, Gc Kabat, Stephanie A. Navarro Silvera, Ab Miller, Te Rohan

Department of Public Health Scholarship and Creative Works

We examined the association of reproductive and hormonal factors with renal cell cancer risk in a cohort study of 89 835 Canadian women. Compared with nulliparous women, parous women were at increased risk (hazard ratio (HR) 1.78, 95% confidence interval (CI) 1.02–3.09), and there was a significant gradient of risk with increasing levels of parity: relative to nulliparous women, women who had X5 pregnancies lasting 4 months or more had a 2.4-fold risk (HR 1⁄4 2.41, 95% CI 1⁄4 1.27–4.59, P for trend 0.01). Ever use of oral contraceptives was associated with a modest reduction in risk. No associations were …

Glycaemic Index, Glycaemic Load And Risk Of Endometrial Cancer: A Prospective Cohort Study, Stephanie A. Navarro Silvera, Thomas E. Rohan, Meera Jain, Paul D. Terry, Geoffrey R. Howe, Anthony B. Miller

Department of Public Health Scholarship and Creative Works

Objective

High-glycaemic-load diets may increase endometrial cancer risk by increasing circulating insulin levels and, as a consequence, circulating oestrogen levels. Given the paucity of epidemiological data regarding the relationship between the dietary glycaemic index and glycaemic load and endometrial cancer risk, we sought to examine these associations using data from a prospective cohort study.

Design, setting, and subjects

We examined the association between dietary glycaemic load and endometrial cancer risk in a cohort of 49 613 Canadian women aged between 40 and 59 years at baseline who completed self-administered food-frequency questionnaires between 1982 and 1985. Linkages to national mortality and …