Acohort study was designed to assess the impact of sun exposure on skin damage in beach volleyball players. during a weekend tournament, players from one team wore waterproof, spf 35 sunscreen, while players from the other team did not wear any sunscreen. at the end of the volleyball tournament players' skin from both teams was analyzed for texture, sun damage, and burns. comparisons of skin damage were then made based on the use of sunscreen. the analysis showed a significant difference between the cohorts in terms of the skin damage. this is the exampe of: