University of Tennessee Health Science Center

About: University of Tennessee Health Science Center is a education organization based out in Memphis, Tennessee, United States. It is known for research contribution in the topics: Population & Medicine. The organization has 15716 authors who have published 26884 publications receiving 1176697 citations.

Assessment and control for confounding by indication in observational studies.

Abstract: In the evaluation of pharmacologic therapies, the controlled clinical trial is the preferred design. When clinical trial results are not available, the alternative designs are observational epidemiologic studies. A traditional concern about the validity of findings from epidemiologic studies is the possibility of bias from uncontrolled confounding. In studies of pharmacologic therapies, confounding by indication may arise when a drug treatment serves as a marker for a clinical characteristic or medical condition that triggers the use of the treatment and that, at the same time, increases the risk of the outcome under study. Confounding by indication is not conceptually different from confounding by other factors, and the approaches to detect and control for confounding--matching, stratification, restriction, and multivariate adjustment--are the same. Even after adjustment for known risk factors, residual confounding may occur because of measurement error or unmeasured or unknown risk factors. Although residual confounding is difficult to exclude in observational studies, there are limits to what this "unknown" confounding can explain. The degree of confounding depends on the prevalence of the putative confounding factor, the level of its association with the disease, and the level of its association with the exposure. For example, a confounding factor with a prevalence of 20% would have to increase the relative odds of both outcome and exposure by factors of 4 to 5 before the relative risk of 1.57 would be reduced to 1.00. Observational studies have provided important scientific evidence about the risks associated with several risk factors, including drug therapies, and they are often the only option for assessing safety. Understanding the methods to detect and control for confounding makes it possible to assess the plausibility of claims that confounding is an alternative explanation for the findings of particular studies.

Effects of conjugated equine estrogen on stroke in the Women's Health Initiative

Abstract: Background— The Women’s Health Initiative (WHI) Estrogen Alone trial assessed the balance of benefits and risks of hormone use in healthy postmenopausal women. The trial was stopped prematurely because there was no benefit for coronary heart disease and an increased risk of stroke. This report provides a thorough analysis of the stroke finding using the final results from the completed trial database. Methods and Results— The WHI Estrogen Alone hormone trial is a multicenter, double-blind, placebo-controlled, randomized clinical trial in 10 739 women aged 50 to 79 years who were given daily conjugated equine estrogen (CEE; 0.625 mg; n=5310) or placebo (n=5429). During an average follow-up of 7.1 years, there were 168 strokes in the CEE group and 127 in the placebo group; 80.3% of strokes were ischemic. For all stroke the intention-to-treat hazard ratio [HR] (95% CI) for CEE versus placebo was 1.37 (1.09 to 1.73). The HR (95% CI) was 1.55 (1.19 to 2.01) for ischemic stroke and 0.64 (0.35, 1.18) for hemorrh...

Unique forms of the abl tyrosine kinase distinguish Ph1-positive CML from Ph1-positive ALL

Abstract: In the Philadelphia chromosome (Ph1) of chronic myelogenous leukemia (CML), the c-abl gene on chromosome 9 is translocated to bcr on chromosome 22. This results in the expression of a chimeric bcr-abl message that encodes the P210bcr-abl tyrosine kinase. The cells of 10% of acute lymphocytic leukemia patients (ALL) carry a cytogenetically similar Ph1 translocation. We report that Ph1-positive ALL cells express unique abl-derived tyrosine kinases of 185 and 180 kilodaltons that are distinct from the bcr-abl-derived P210 protein of CML. The appearance of the 185/180-kilodalton proteins correlates with the expression of a novel 6.5-kilobase messenger RNA. Thus, similar genetic translocations in two different leukemias result in the expression of distinct c-abl-derived products.