this suggests that highskilled individuals skills decline more slowly with age than do those of lowskilled individuals though it is not possible to know this with certainty without longitudinal data additionally two studies using these data have demonstrated a large causal impact of schooling on skills additionally both studies provide some evidence of differential impact of schooling reforms hi a correlational analysis green and riddell observe that schooling is more strongly associated with skills at the tenth skills percentile in canada norway and the us in his instrumental variables iv analysis din er shows that the causal effect of additional schooling is greater at the lower end of the skills distribution both results imply that educational expansion promotes equity