53. Investigators are interested in the effect of TV watching on obesity rates a

Question

53. Investigators are interested in the effect of TV watching on obesity rates among young children. They therefore conducted a cohort study in which they enrolled over 1 million children ages 0 - 23 months in 2008. At the baseline assessment, they asked parents to report the average number of hours of TV the children watched each day. They then followed up with the children 2-3 years later in 2010 and 2011 to assess their BMI (and incidence of obesity). Investigators found an incidence rate of obesity of 14 cases per 100 person-years among children who watched 2 hours or more of TV per day and 8 cases per 100 person-years among children who watched less than 2 hours of TV per day. The overall incidence rate of obesity among this population in the U.S. is estimated to be 10 cases per 100 person-years. What risk could be eliminated from the population if young children stopped watching TV for more than 2 hours each day? A. 2 cases per 100 person-years B. 43% C. 20% D. 6 cases per 100 person-years E. 14%

Explanation / Answer

Solution:

Option A is correct.

If young children stopped watching TV for more than 2 hours each day, 2 cases per 100 person-years could be eliminated.

Two hours or more: 14 cases per 100 person-years.

Less than two hours: 8 cases per 100 person-years.

Overall: 10 cases per 100 person-years.

8x + 14(1-x) = 10

8x + 14 - 14x = 10

x = 2/3

1-x = 1/3

Thus, 1/3(14 - 8) = 1/3(6) = 2 cases per 100 person-years.

(Since, 14 per 100 are being reduced to 8 per 100 when they stop watching TV for 2 or more hours per day and the weight of 14 per 100 is 1/3, we multiplied 6 with 1/3).

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