Data Collectionmedium
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A longitudinal study begins with 500 participants to examine the relationship between physical activity in young adulthood and health outcomes in middle age. After 1 year, 480 remain (96% retention). After 2 years, 420 remain (84% retention). Analysis shows the remaining 420 have significantly higher education levels and higher average incomes than the original 500. Which statement best describes the threat to validity?
A longitudinal study begins with 500 participants to examine the relationship between physical activity in young adulthood and health outcomes in middle age. After 1 year, 480 remain (96% retention). After 2 years, 420 remain (84% retention). Analysis shows the remaining 420 have significantly higher education levels and higher average incomes than the original 500. Which statement best describes the threat to validity?