use a test t A psychologist wanted to know if customers really are influenced to buy more by sales clerks who smile more than clerks who do not smile more. To test this hypothesis, clerks at eight stores in a large clothing chain were given special instructions at the start of a week, and then sales over the week were recorded. Four of the stores were randomly selected to have the clerks receive instructions to be especially courteous and to smile a lot (Smile Condition). Clerks at the other four stores were instructed to be especially courteous only (Control Condition). The mean sales (in thousands of dollars) for the clerks in the four stores in the Smile Condition was 39 (SS = 44), and the mean sales for the clerks in the four stores in the Control Condition was 32 (SS = 94). a. What is the independent variable in this study? b. What is the dependent variable in this study? c. Define the populations. d. What is the psychologist's research hypothesis (in words and symbols)? e. What is the psychologist's null hypothesis (in words and symbols)? f. What type of distribution is the comparison distribution? g. What are the three characteristics of the comparison distribution? h. What is the t score cut-off on the comparison distribution? (Use the .05 significance level.) i. What is the sample's t score on the comparison distribution? n. Figure the 95% confidence interval around the difference between the mean of the stores instructed to be especially courteous and smile a lot and the mean of the stores instructed to be especially courteous only. o. In terms of this study, what does the confidence interval tell the psychologist? p. Explain how the psychologist could use the confidence interval to make decisions about the hypotheses in (j.).