Question

Loftus and Palmer study (1974) demonstrated the influence of language on eyewitness memory. Participants watched a film of a car accident and were asked questions about what they saw. One group was asked “About how fast the cars were 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”. The ‘smasher into” group reported significantly higher estimates of speed than the hit group. Suppose a researcher repeats this study with two samples of college students and obtains the following results:

Estimated Speed
Smashed into	hit
n = 15	n = 15
M = 40.8	M = 34.0
SS = 510	SS = 414

Is there a significantly higher estimate speed for the “smashed into” group? Use a one-tailed test with α = .01.

1. Compute the estimated value for Cohen’s d to measure the size of the effect.

2. Use the data to make a 99% confidence interval estimate of the mean difference in estimate speed between the “smashed into” group and the “hit” group

3. Use the data to make a 99% confidence interval estimate of the mean difference in estimate speed between the “smashed into” group and the “hit” group

4.Report the results of the hypothesis test in APA. As a measure of the effect size use the confidence interval.

Answer 1

first, we will calculate the sample standard deviation

Let the Smashed into be the sample 1:

Let Hit be the sample 2

we will write the hypothesis

the alternate hypothesis

Hence we have evidence that a significantly higher estimate speed for the “smashed into” group.

1) cohen's d formula is

2) the confidence interval formula is

for 99% confidence and df= smallest of df1 and df2 i.e = 15-1=14

4) since the confidence interval is not including 0 we are confident to reject the null hypothesis