Intraclass Correlation Coefficients for Planning Cluster Randomized Trials in Community-Dwelling Older Adults.

OBJECTIVES: With the emerging trends, more cluster randomized trials will be conducted in older adults, where facilities are randomized rather than individuals. Similarity of individuals from a facility (intraclass correlation coefficient/ICC) plays a critical role, but not readily available. We document ICCs for measures commonly used in community-dwelling older adults and discuss implications.

METHOD: Secondary analysis of a range of baseline measures from the On the Move cluster randomized trial, whose ICCs were computed using a linear mixed model.

RESULTS: Self-reported disability measures related to facility characteristics and sense of community had the greatest ICCs (>0.10), while mobility performance measures had 0.05 to 0.10, and cognitive measure 0.11.

DISCUSSION: The ICCs for measures commonly used in older adults are of a sufficient magnitude to have a substantial impact on planned sample size of a study and credibility of results, and should be taken into consideration in study planning and data analysis.