In several of the following exercises, you are asked to identify the type of data that is described. Possible answers include anecdotal data, available data, observational data that are from sample surveys, observational data that are not from sample surveys, and experiments. It is possible for some data to be classified in more than one category.
3.11 Marketing milk.
An advertising campaign was developed to promote the consumption of milk by adolescents. Part of the campaign was based on a study conducted to determine the effect of additional milk in the diet of adolescents over a period of 18 months. A control group received no extra milk. Growth rates of total body bone mineral content (TBBMC) over the study period were calculated for each subject. Data for the control group were used to examine the relationship between growth rate of TBBMC and age.
3.11
(a) This is an experiment. Groups were chosen to receive extra milk or not. (b) The control group data alone are observational because there was no treatment imposed of additional milk. (c) TBBMC is the response. Age is not the explanatory variable; it functions as a control variable. The treatment of “additional milk” is the explanatory variable.