Final answer:
The strongest evidence linking physical exercise to successful cognitive aging is correlational, based on observational studies showing individuals who exercise regularly are less likely to develop dementia.
Step-by-step explanation:
The strongest evidence supporting a relationship between physical exercise and successful cognitive aging is best described as correlational. This conclusion is based on observational studies which have established a correlation where individuals who engaged in regular physical exercise had a lower incidence of dementia compared to those who did not. However, while these studies show a strong correlation, they do not definitively prove causation due to the potential for other variables to influence the outcome.
The cited study by Larson et al. (2006) supports this correlation, showing that people aged 65 or older who exercised regularly had a reduced risk for developing dementia. Longitudinal research further strengthens this association by following subjects over an extended period and collecting data that can highlight the cognitive benefits of physical exercise.