Is day-to-day variability in cognitive function coupled with day-to-day variability in affect?

Intra-individual differences in cognitive function that occur reliably across repeated assessment occasions are thought to correspond to contemporaneous fluctuations in affect. However, the empirical evidence for this hypothesis is to date inconclusive. Here, a sample of 98 participants was recruited to complete tests of short-term memory, processing speed, and working memory, as well as rating daily their positive and negative affect (PANAS), on each of five consecutive days. Cognitive tests' re-test correlations averaged at .72; for affect, test re-test correlations averaged .53. The within-person variability in cognitive tests was overall smaller (13.5% for both working memory and short-term memory, and 16% for processing speed) than in affect (24% for positive and 51.7% for negative affect). A series of linear mixed effects models showed that day-to-day-variability in cognitive function was not coupled with contemporaneous fluctuations in positive and negative affect (i.e. states; ns in all cases). Thus, affect and cognitive function fluctuate within individuals across days but they appear to do so independently of one another.