Should you adjust for baseline characteristics within randomized controlled trials?

At first glance, one may think the answer is no. Randomization should insure that baseline characteristics are balanced across trial arms. In practice, however, sometimes baseline characteristics due differ somewhat by trial arm simply by chance, especially in smaller randomized controlled trials (RCTs). A JAMA Guide to Statistics and Methods by Holmberg et al. 2022…

What is collider bias?

A paper by Holmberg et al. (2022) in JAMA provides a number of examples of how collider bias can lead to problematic causal inference. The term collider bias is often invoked when using directed acyclic graphs (DAGs) to map the causal pathway. Collider bias occurs when you aim to measure the impact of A on…

How to justify your survival curve extrapolation methodology

Clinical trials are typically of (relatively) short duration, but innovative treatments may impact patient survival over multiple years. Health economists and outcomes researchers often are faced with the challenge of extrapolating clinical trial survival curves to estimate long-term survival gains for the typical patient. These estimates may be done parameterically (e.g., exponential, Weibull, Gompertz, log-logistic,…

Who pays for health care? Who uses it?

Ultimately, individuals and households pay for health care. Whether payments are made directly to providers, via taxes or through commercial insurance, households are the sole source of health care financing. Further, all treatments are ultimately provided on behalf of individuals and households. A key question, however, is which types of individuals pay more for health…

Survival distributions in R

My former colleague Devin Incerti has a nice summary of how to implement survival function estimation in R. Not only does he mathematically describe the probability density function (PDF), cumulative density function (CDF), and hazard rates for 8 commonly used parametric survival curves [see table below], he also describes how to implement these using the…