Question

An experiment was done to test the effectiveness of a drug that is being considered for possible use in the treatment of people who experience chronic anxiety. Fifty people who are chronically anxious are identified through a local health clinic, and all 50 people give their informed consent to participate in the experiment. Twenty-five people are randomly assigned to the experimental group, and they receive the new drug. The other 25 people are randomly assigned to the control group, and they receive the commonly used drug. The participants in both groups are monitored by a physician and a clinical psychologist during the 6-week treatment period. After the treatment period, the participants provide a self-rating on a reliable and valid 20-point scale indicating the level of anxiety they are experiencing (higher scores indicate greater anxiety).

The mean self-rating in the experimental group was 10.2 (SD = 1.5), and the mean rating in the control group was 13.5 (SD = 2.0).

The .95 confidence interval for the mean self-rating in the experimental group was 9.6 to 10.8.

The .95 confidence interval for the control group was 12.7 to 14.3.

(1) Explain why a double-blind procedure would be useful in this experiment, and describe how the double-blind procedure could be carried out in this experiment.

     

(2) Focus on the descriptive statistics for this experiment. How would you describe the effect of the drug variable on anxiety ratings using the means for each condition? What do the standard deviations tell you about the anxiety ratings in the experiment?

     

(3) The probability associated with the test for the mean difference between the two groups was p = .01. What claim would you make about the effect of the treatment based on this probability? What claim would you make based on the estimates of the population means for the two groups in this experiment based on a comparison of the confidence intervals?

     

(4) The effect size for this experiment is d = .37. What information does this effect size tell you about the effectiveness of the drug beyond what you know from the test of statistical significance and from comparing the confidence intervals?

                 

Answer 1

(1) The double-blind procedure would be useful in this experiment because this will help us to completely randomize the experiment that will vanish the bias that might be introduced by experimenters and participants. This could be carried out in the following way:

1. Randomly select 25 participants for new drug and commonly used drug then assign the participants but don’t tell the participants regarding which drug they are being assigned to.

2. Physician and clinical psychologist will have to monitor them during a 6-week period but they won’t be informed that which group they are going to monitor.

This will be a double-blind experiment because participants and experimenters do not know about the drugs.

(2) Based on the provided descriptive statistics, anxiety rating by the experimental group is less than the anxiety ratings by the control group but the variation in the experimental group is lower than the variation in the control group.

(3) Based on the given probability, we can claim that there exists a significant difference between the population means of the experimental and control group because this probability is less than the level of significance if considered 0.05. Also, based on the confidence interval we can claim that there exists a significant difference between the population means of the experimental and control group because the two confidence intervals do not coincide.

(4) The effect size is 0.37 that means there is a small effect of the difference between the means of the two groups. Also, the statistical significance based on the test and confidence interval says that there exists a significant difference between the two groups, the effect size claims that the difference is not very effective.

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