Classifying medical histories in US Medicare beneficiaries using fixed vs all‐available look‐back approaches

• Published in: Pharmacoepidemiology and drug safety Vol. 27; no. 7; pp. 771 - 780
• Main Authors: Conover, Mitchell M., Stürmer, Til, Poole, Charles, Glynn, Robert J., Simpson, Ross J., Pate, Virginia, Jonsson Funk, Michele
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.07.2018
• Subjects: administrative claims; Aged; Beneficiaries; bias; Cancer; Cardiovascular diseases; classification; Confounding (Statistics); confounding variables; epidemiologic methods; Government programs; health care; Health risks; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors - administration & dosage; Initiators; Longitudinal studies; Medical Records; Medicare; Mortality; North Carolina; pharmacoepidemiology; United States; North Carolina; United States; database; epidemiologic methods; confounding variables; bias; administrative claims; classification; health care; longitudinal studies; pharmacoepidemiology
• ISSN: 1053-8569; 1099-1557
• DOI: 10.1002/pds.4435

Purpose Evaluate use of fixed and all‐available look‐backs to identify eligibility criteria and confounders among Medicare beneficiaries. Methods We identified outpatient visits (2007‐2012) with recently documented (≤180 days) cardiovascular risk and classified patients according to whether the exposure (statin) was initiated within 14 days. We selected each beneficiary's first eligible visit (in each treatment group) that met criteria during the respective look‐backs: continuous enrollment (1 or 3 years for fixed look‐back; 180 days for all‐available), no cancer history, and no statin claims. We estimated crude and standardized mortality ratio weighted hazard ratios (HRs) for the effect of statin initiation on incident 6‐month cancer (a known null effect) and 2‐year mortality, separately, adjusting for covariates assessed by using each look‐back. Results Analyzing short‐term cancer, the estimated HR from the all‐available approach (HR = 0.90, 95% CI: 0.83, 0.98) was less biased than the 1‐year look‐back (HR = 0.79, 95% CI: 0.73, 0.84), which included beneficiaries with prevalent cancer. The 3‐year look‐back (HR = 1.05, 95% CI: 0.90, 1.21) was somewhat less biased than the all‐available estimate but less precise due the exclusion of a large proportion of observations without sufficient continuous enrollment (62.0% and 59.9% of initiators and non‐initiators, respectively). All approaches produced similar estimates of the effect on all‐cause mortality. Alternative look‐backs did not differ in their ability to control confounding. Conclusions The all‐available look‐back performed nearly as well as the 3‐year fixed, which produced the least biased point estimate. If 3‐year look‐backs are infeasible (eg, due to power/sample), all‐available look‐backs may be preferable to short (1‐year) fixed look‐backs.