Response to Yang and Chan. Metformin and the Risk of Cancer: Time-Related Biases in Observational Studies. Diabetes Care 2012;35:2665–2673
- Samy Suissa, PHD1,2 and
- Laurent Azoulay, PHD1,3
- 1Centre for Clinical Epidemiology, Jewish General Hospital, Montreal, Canada
- 2Department of Epidemiology and Biostatistics and Department of Medicine
- 3Department of Oncology, McGill University, Montreal, Canada
- Corresponding author: Samy Suissa, samy.suissa{at}mcgill.ca.
Yang and Chan (1) express uncertainty regarding immortal time bias, an established and rigorously founded principle in epidemiology and statistical sciences, and use data from the Hong Kong Diabetes Registry to quantify the effect of statin use on cardiovascular outcomes. Using the time-fixed approach, known to introduce immortal time bias, they find that statin use is associated with a 34% reduction in cardiovascular events, while the proper time-dependent approach led to a 47% increase in cardiovascular events. Unfortunately, observational research is not this simple. Two elements of the reasoning are untenable.
First, the time-fixed approach in these types of studies is simply erroneous. By this approach, a patient who was …
In this Issue
June 2013, 36(6)
Response to Yang and Chan. Metformin and the Risk of Cancer: Time-Related Biases in Observational Studies. Diabetes Care 2012;35:2665–2673
