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Illustration of modeling the active intervention (30 mg β-carotene plus 25,000 IU retinyl palmitate daily) and placebo during (1988-1995) and after (1996-2005) the β-Carotene and Retinol Efficacy Trial (CARET). “CARET active intervention” was modeled as time-dependent covariate with a 3-year extended effect in the post-intervention phase.
