The memory performance task was included as part of a larger battery of cognitive tasks that was administered by computer-assisted telephone interview. Participants were presented with a word list (15 words, e.g., “drum”, “farmer”, “moon”), with a one-second interval between each word. Both immediate and delayed recall were measured by asking participants to repeat back as many words as they could remember. Immediate and delayed recall were combined into a single composite of memory performance and are presented in standard deviation (z-score) units. More details regarding this task can be found on the MIDUS Cognitive Project webpage (Ryff & Lachman, 2017) and in other publications (e.g., Stephan et al., 2014).

Resting Heart Rate Variability (HRV).

To assess cardiovascular health, we examined resting high-frequency heart rate variability (HRV), which was measured during the MIDUS Biomarker Project. HRV was measured in two 300-sec epochs. Due to the high correlation between HRV measurements (r = 0.93), the two were averaged, and log transformed values are presented in this paper and used in the analyses. For details regarding HRV measurements and data collection, see details on the MIDUS Bio) and work by Dienberg Love et al. (2010). Respiration was also measured; however, results for HRV did not change appreciably when controlling for respiration.

Covariates.

For the purposes of this paper, selected covariates were those related to key demographic dimensions and those that were plausibly related to our outcomes. The majority of the covariates selected have been used in prior publications analyzing data from the Cognitive and Bio; D.