A large, prospective cohort study tracks a population over 2…
A large, prospective cohort study tracks a population over 20 years to investigate the link between long-term exposure to fine particulate matter (PM2.5) and the incidence of chronic obstructive pulmonary disease (COPD). The study produces the following findings: Compared to individuals in the lowest category of PM2.5 exposure, those in the highest category have a threefold higher risk of developing COPD. The risk of COPD increases steadily and progressively with each higher category of PM2.5 exposure. Which of the Bradford Hill criteria for causality is best illustrated by the second finding, and why?