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Combining extant datasets with differing outcome measures, an economical method to generate evidence guiding older adults' cancer care, may introduce heterogeneity leading to invalid study results. We recently conducted a study combining extant datasets from five oncology nurse-directed clinical trials (parent studies) using norm-based scoring to standardize the differing outcome measures. The purpose of this article is to describe and analyze our methods in the recently completed study. Despite addressing and controlling for heterogeneity, our analysis found statistically significant heterogeneity (p < 0.0001) in temporal trends among the five parent studies. We concluded that assessing heterogeneity in combined extant datasets with differing outcome measures is important to ensure similar magnitude and direction of findings across parent studies. Future research should include investigating reasons for …