Does posting calorie content for menu items affect people's choices in fast food restaurants? According to results obtained by Elbel, Gyamfi, and Kersh (2011), the answer is no. The researchers monitored the calorie content of food purchases for children and adolescents in four large fast food chains before and after mandatory labeling began in New York City.
Although most of the adolescents reported noticing the calorie labels, apparently the labels had no effect on their choices. Data similar to the results obtained show an average of M = 786 calories per meal with
s = 85 for n = 100 children and adolescents before the labeling, compared to an average of M = 772 calories with σ = 91 for a similar sample of n = 100 after the mandatory posting.
a. Use a two-tailed test with a = .05 to determine whether the mean number of calories after the posting is significantly different than before calorie content was posted.
b. Calculate r2 to measure effect size for the mean difference.