Length of look-back periods in studies using administrative data: a scoping review

Administrative data, including electronic health record (EHR) and claims data, are increasingly used to generate real-world evidence for epidemiologic research. Unlike clinical trials, which assess baseline conditions at the initial visit, observational studies using these data must define an appropriate lookback period to identify baseline characteristics. However, no established guidelines exist on the optimal length of lookback periods by clinical outcome. We conducted a scoping review, with a lens on methodological studies, to assess the frequency and variability of lookback periods used in epidemiologic studies. We searched PubMed for studies that employed lookback periods using EHR, claims data, or international registries. Our search yielded 262 studies spanning a broad range of clinical outcomes. We found that lookback periods varied significantly, ranging from 12 hours to 39 years, depending on the clinical outcome. The most common clinical areas included pharmacology, cardiovascular disease, cancer, and healthcare utilization. Our review underscores the need for tailored lookback periods based on the clinical context and suggests that a one-size-fits-all approach may be inadequate. Future research should focus on the impact of lookback periods on less-studied outcomes. This review provides a resource for researchers to make informed decisions on the appropriate lookback periods in epidemiologic studies utilizing administrative data.