Latest Publications

Our faculty’s research is frequently accepted for inclusion in the most prestigious peer-reviewed scientific journals, with over 330 articles published in 2015 alone. Below you will find the most recent publications.

The abstracts below are updated daily. For a more complete list, please visit this PubMed link.

Estimating the effect of immortal-time bias in urologic research: a case example of testosterone-replacement therapy.

Estimating the effect of immortal-time bias in urologic research: a case example of testosterone-replacement therapy.

BJU Int. 2017 May 26;:

Authors: Wallis CJD, Saskin R, Narod SA, Law C, Kulkarni GS, Seth A, Nam RK

OBJECTIVE: To quantify the effect of immortal-time bias in an observational study examining the effect of cumulative testosterone exposure on mortality.
SUBJECTS AND METHODS: We used a population-based matched cohort study of men aged 66 and older newly treated with testosterone replacement therapy and matched-controls from 2007-2012 in Ontario, Canada to quantify the effects of immortal-time bias. We used generalized estimating equations to determine the association between cumulative testosterone replacement therapy exposure and mortality. Results produced by models using time-fixed and time-varying exposures were compared. Further, we undertook a systematic review of PubMed to identify studies addressing immortal-time bias or time-varying exposures in the urologic literature and qualitative summated these.
RESULTS: Among 10,311 TRT-exposed men and 28,029 controls, the use of a time-varying exposure resulted in the attenuation of treatment effects compared with an analysis which did not account for immortal-time bias. While both analyses showed a decreased risk of death for patients in the highest tertile of TRT exposure, the effect was overestimated when using a time-fixed analysis (aHR 0.56, 95% CI 0.52-0.61) when compared to a time-varying analysis (aHR 0.67, 95% CI 0.62-0.73). Of the 1241 studies employing survival analysis identified in the literature, nine manuscripts met criteria for inclusion. Of these, 5 employed time-varying analytic methodology. Each of these was a large, population-based retrospective cohort study assessing potential harms of pharmacologic agents.
CONCLUSIONS: Where exposures vary over time, a time-varying exposure is necessary to draw meaningful conclusions. Failure to employ a time-varying analysis will result in overestimation of a beneficial effect. However, time-varying exposures are uncommonly utilized among manuscripts published in prominent urologic journals. This article is protected by copyright. All rights reserved.

PMID: 28548282 [PubMed - as supplied by publisher]