On the Causal Interpretation of Rate-Change Methods: The Prior Event Rate Ratio and Rate Difference.

ABSTRACT: A growing number of studies use data before and after treatment initiation in groups exposed to different treatment strategies to estimate "causal effects" using a ratio measure called the prior event rate ratio (PERR). Here, we offer a causal interpretation for PERR and its additive scale analog, the prior event rate difference (PERD). We show that causal interpretation of these measures requires untestable rate-change assumptions about the relationship between 1) the change of the counterfactual rate before and after treatment initiation in the treated group under hypothetical intervention to implement the control strategy; and 2) the change of the factual rate before and after treatment initiation in the control group. The rate-change assumption is on the multiplicative scale for PERR b

SUBMITTER: van Aalst R 

PROVIDER: S-EPMC7784529 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature