Invited Commentary: Why use methods that require proportional hazards?

We recently questioned the utility of testing for proportional hazards in survival analysis. Here we expand on why the proportional hazards assumption is both implausible and unnecessary in most medical studies, particularly in randomized trials. We conclude that using survival analysis methods that do not rely on proportional hazards is typically the preferred course of action.

A Structural Description of Biases That Generate Immortal Time.

Immortal time may arise in survival analyses when individuals are assigned to treatment strategies based on post-eligibility information or selected based on post-assignment eligibility criteria. Selection based on eligibility criteria applied after treatment assignment results in immortal time when the analysis starts the follow-up at assignment. Misclassification of assignment to treatment strategies based on treatment received after eligibility results in immortal time when the treatment strategies are not distinguishable at the start of follow-up.

Prostate-Specific Antigen Screening and Prostate Cancer Mortality: An Emulation of Target Trials in US Medicare.

Purpose: No consensus about the effectiveness of prostate-specific antigen (PSA) screening exists among clinical guidelines, especially for the elderly. Randomized trials of PSA screening have yielded different results, partly because of variations in adherence, and it is unlikely that new trials will be conducted. Our objective was to estimate the effect of annual PSA screening on prostate cancer (PC) mortality in Medicare beneficiaries age 67-84 years.

Estimating the Effect of Bariatric Surgery on Cardiovascular Events Using Observational Data?

Background: Observational studies have reported strongly protective effects of bariatric surgery on cardiovascular disease, but with oversimplified definitions of the intervention, eligibility criteria, and follow-up, which deviate from those in a randomized trial. We describe an attempt to estimate the effect of bariatric surgery on cardiovascular disease without introducing these sources of bias, which may not be entirely possible with existing observational data.

Methods: We propose two target trials among persons with diabetes: (1) bariatric operation (vs.