All cognitive scores reported above involve processing speed as a significant factor, consistent with previous studies27. However, the observation that different test scores do not all correlate identically with each other or with the same brain IDPs suggests that there is not a single (speed-related) cognitive factor at play. The increases in association strengths when not controlling for age suggest that age-related cognitive decline is a major source of cross-subject variability for these IDP-cognition associations28. Plotting all IDP-cognitive associations (Fig 6c) demonstrated that a large number of non-age-adjusted associations (gray circles) were stronger than the results after age adjustment (colored circles); below, we show how interpretation of such results can be aided further through multivariate analyses. These age interactions provide an early indication that UK Biobank should provide cognitive biomarkers of clinical significance as health outcomes accumulate.
