SECTION 1.3 Data Collection and Experimental Design 25 Using and Interpreting Concepts 19. Acne Treatment A company wants to test the effectiveness of a new acne cream. The company recruits 500 girls ages 13 to 17 who have acne. The subjects are randomly assigned into two groups. One group is given the acne cream and the other is given a placebo that looks exactly like the acne cream. Both groups apply the cream daily for two months. Facial photos are taken at the beginning and end of the treatment to compare results. (a) Identify the experimental units and treatments used in this experiment. (b) Identify a potential problem with the experimental design being used and suggest a way to improve it. (c) How could this experiment be designed to be double-blind? 20. Social Anxiety Disorder Researchers in Japan tested the effect of cannabidiol (CBD) in treating late teenagers with social anxiety disorder (SAD). Thirty-seven 18- to 19-year-old teenagers with SAD took part in the study. The patients were assigned at random to receive a daily dose of either CBD or a placebo for 4 weeks. Symptoms were measured using The Fear of Negative Evaluation Questionnaire and the Liebowitz Social Anxiety Scale at the beginning and end of the treatment. (Source: Frontiers in Psychology) (a) Identify the experimental units and treatments used in this experiment. (b) Identify a potential problem with the experimental design being used and suggest a way to improve it. (c) The experiment is described as a placebo-controlled, double-blind study. Explain what this means. (d) How could blocking be used in designing this experiment? 21. Sleep Deprivation A researcher wants to study the effects of sleep deprivation on motor skills. Eighteen people volunteer for the experiment: Jake, Arya, Xavier, Nyla, Shaniece, Chen, Juan, Hana, Nia, Ansel, Liam, Bruno, Mei, Zoey, Kayla, Liam, Sofia, and Kai. Use a random number generator to choose nine subjects for the treatment group. The other nine subjects will go into the control group. List the subjects in each group. Tell which method you used to generate the random numbers. 22. Using a Simple Random Sample Volunteers for an experiment are numbered from 1 to 90. The volunteers are to be randomly assigned to two different treatment groups. Use a random number generator different from the one you used in Exercise 21 to choose 45 subjects for the treatment group. The other 45 subjects will go into the control group. List the subjects, according to number, in each group. Tell which method you used to generate the random numbers. Identifying Sampling Techniques In Exercises 23–28, identify the sampling technique used, and discuss potential sources of bias (if any). Explain. 23. Selecting students at random from a campus directory, researchers contact 300 people and ask what obstacles (partying is mentioned as an example) keep them from completing their homework. 24. Questioning university students as they leave a college cafeteria, a researcher asks 342 students about their eating habits. 25. After a hurricane, a disaster area is divided into 200 equal grids. Thirty of the grids are selected, and every occupied household in the grid is interviewed to help focus relief efforts on what residents require the most.
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