Within- and Between-Person Differences in Activity Factor Structure: Results From an Ecological Momentary Assessment Study.

Objectives: Studies using ecological momentary assessment (EMA) of activity participation rely on items tapping domains informed by factor analyses based on single time points. Analyses from a single time point focus on differences between participants and provide little insight into how activities cluster together within a person across moments or days. The present study compared the factor structure in activity participation between- and within-persons using an expanded set of momentary activity items in middle and older adulthood.

Methods: Using tablets, 81 adults aged 41 to 94 years reported activities completed in the past 3-4 hr 5 times per day for 14 days.

Results: The most common activities during the day involved social interactions, reading, and computer work. Watching TV or videos was the most common evening activity. Multilevel factor analysis simultaneously computed both intra-individual factors (within-person) and inter-individual factors (between-person). Four within-person and 4 between-person factors provided the best model fit, with 3 common factors: cognitive (read, computer); social (events, mentoring, providing care); and passive (TV, games). There were notable differences in the fourth factor.

Discussion: Although three common activity factors were found between individuals and within persons from day to day, the divergence between the fourth intra- and inter-individual factors provides insight into how activity engagement operates at different timescales and likely reflects daily demands versus long-term goals. EMA provides a window into engagement throughout and across days, but researchers who commonly use retrospective reports of between-person activity engagement may find distinctly different results from factor analyses.