A researcher is interested in how the language used to ask a question can influence eyewitness memory. In her study, college students watched a film of an automobile accident and then were asked questions about what they saw. One group was asked, “About how fast were the cars going when they smashed into each other?” Another group was asked the same question except the verb was changed to “hit” instead of “smashed into.” Below are her results:

Estimated Speed

“Smashed into” group     “Hit” group

n = 15                                   n = 15

xbar = 40.8                         xbar = 34.9

SS = 510                               SS = 414

Use the two-sample t-test to determine whether the wording of the question affected participants’ estimates of speed.

1. State the null and alternate hypotheses in symbols

2. What critical value should be used to test the hypothesis with = .01?

3. Calculate the two-sample t-statistic

4. What decision should the researcher make about the null hypothesis?

5. Calculate Cohen's d.

6. What conclusion should the researcher reach about the effect of questions wording on participants’ estimates of speed?