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CHAPTER 6: Independent Groups Designs 223present across a wide range of ages—thus, theheadline.A Why is the newspaper headline for this articlepotentially misleading?B Why do you think the researchers tested onlymen?C Identify two different ways of obtaining evidencethat you could use to decide whether the resultsof this study could be applied to women. One ofthe ways would make use of already publishedresearch, and the other way would require doinga new study.4 An experiment was done to test the effectivenessof a new drug that is being considered for possibleuse in the treatment of people who experiencechronic anxiety. Fifty people who are chronicallyanxious are identified through a local health clinic,and all 50 people give their informed consentto participate in the experiment. Twenty-fivepeople are randomly assigned to the experimentalgroup, and they receive the new drug. The other25 people are randomly assigned to the controlgroup, and they receive the commonly used drug.The participants in both groups are monitoredby a physician and a clinical psychologist duringthe 6-week treatment period. After the treatmentperiod, the participants provide a self-rating on areliable and valid 20-point scale indicating the levelof anxiety they are experiencing (higher scoresindicate greater anxiety). The mean self-rating inthe experimental group was 10.2 (SD 1.5),and the mean rating in the control group was13.5 (SD 2.0). The .95 confidence interval forthe mean self-rating in the experimental groupwas 9.6 to 10.8. The .95 confidence interval forthe control group was 12.7 to 14.3.A Explain why a double-blind procedure would beuseful in this experiment, and describe how thedouble-blind procedure could be carried out inthis experiment.B Focus on the descriptive statistics for thisexperiment. How would you describe the effectof the drug variable on anxiety ratings usingthe means for each condition? What do thestandard deviations tell you about the anxietyratings in the experiment?C The probability associated with the test forthe mean difference between the two groupswas p .01. What claim would you makeabout the effect of the treatment based on thisprobability? What claim would you make basedon the estimates of the population means forthe two groups in this experiment based on acomparison of the confidence intervals?D The effect size for the treatment variable in thisexperiment is d .37. What information doesthis effect size tell you about the effectivenessof the drug beyond what you know from the testof statistical significance and from comparingthe confidence intervals?Answer to Stretching Exercise I1 Bushman (2005) manipulated the independent variable of type of television program in hisstudy. There were four levels of the independent variable: violent, sexually explicit, violent andsex, and neutral.2 Bushman (2005) held several factors constant: the same advertisements were used in each condition,participants were tested in small groups in the same setting, and ads were placed atapproximately the same point in each program.3 Bushman (2005) balanced the characteristics of the participants across the four levels by randomlyassigning participants to conditions. Thus, participants in each level were equivalent,on average, in their memory ability and their exposure to television programs and products.Bushman also used two random orders of the ads to balance any potential effects due to placementof the ads during the TV programs.Answer to Stretching Exercise II1 When one of your authors completed this exercise, she obtained a mean value of 5.65 for theexperimental group and a mean of 5.35 for the control group. The two groups were approximatelyequivalent in terms of average memory ability (a t-test could be computed to determine if themean scores differ statistically).2 The experimental group had three “participants” with scores of 2 (and no aces). When these weredropped, the new mean for memory ability was 6.4. Compared to the control group mean of 5.35,the experimental group had, on average, greater memory ability following selective subject loss.