Exam 1: Collecting Data in Reasonable Ways

A placebo is designed to be identical in appearance to the treatment of interest, but contains no active ingredients.

After reading the description below, determine whether the study is an observational or experimental study. Justify your answer with specific references to the information in the study. "We compared paired daytime and night counts of wild brook trout, brown trout, and rainbow trout made by the same snorkelers in five streams during August. Overall, we counted 109 trout in the daytime and 333 trout at night. We speculate that trout counted at night were present during the daytime but were hidden from view. Biologists should consider that trout behavior and visibility might vary between daytime and night, even during summer. In some streams, the majority of trout may not be seen during the daytime."

If the subjects as well as the person measuring the response are aware of the treatment assigned to the subject, only single-blinding is being used.

River City is seeking to compare the effects of two mosquito sprays, A and B, to be used in the insect control plan for their park system. Consider the following two plans for a statistical study: • In Plan #1, a simple random sample of plots of park land would be taken from the population of River City parks. Either treatments A or B would be randomly assigned to each of the plots. • In Plan #2, simple random samples of plots of park land would be taken from each of four geographic areas in River City. (River City has 4 geographic areas of town, the NE, NW, SE, and SW quadrants.) Either treatments A or B would be randomly assigned to each of the plots within each geographic area. a) Consider study plan #1: i) Would it be appropriate to infer a cause-and-effect relationship if the results of the two treatments differ? Why or why not? ii) Could the results be generalized to all areas of the park land? Why or why not? b) Consider study plan #2: i) Would it be appropriate to infer a cause-and-effect relationship if the results of the two treatments differ? Why or why not? ii) Could the results be generalized to all areas of the park land? Why or why not?