Question

In 1974, Loftus and Palmer conducted a classic study demonstrating how the language used to ask a question can influence eyewitness memory. In the 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.” The “smashed into” group reported significantly higher estimates of speed than the “hit” group. You, as a researcher wonder if Loftus and Palmer’s study is reliable, and repeats this study with a sample of FIU students and obtains the following data.

Hit Group	Smashed Into Group
32	50
26	44
40	54
23	45
42	44
20	40
37	49
25	34
24	38
22	30
19	50
24	46
19	40
22	35
29	43
24	41
34	30
33	39
37	44
20	35

Your job is to determine if smashed into group reports higher speed than hit group. As you work on this problem, make sure to provide information for each of the eight steps we cover in Chapter 11 (Salkind) as well as the APA write-up you would see in a results section.

1. State the null and alternative hypotheses
2. Tell me your level of risk
3. Determine the best statistical test to use
4. Determine the value needed to reject the null hypothesis. Remember to calculate the correct degrees of freedom before finding the critical t-value! Note whether it is best to use the one-tailed or two-tailed test.
5. Compare the obtained and critical value
6. Decide whether you will retain the null hypothesis or …
7. Decide whether you will reject the null hypothesis
8. Finally, write up your results as you would see it in a results section of an empirical research paper. Make sure to include the means and SDs for smashed into and hit group (in miles). I do NOT need to see the effect size (Cohen’s D)
9. Was your obtained t-value positive or negative? Would it matter either way? With your discussion group, tell my why a positive or negative value is not important when it comes to your obtained value
10. What is more appropriate to use for your data set: the one-tailed t-Test or the two-tailed t-Test. Why? Would your APA write-up differ depending on which you used?
11. Why would it be easier to find significance using a p value of .05 than a p value of .01?
12. Finally (and this is the tough one), how would your results have differed with regard to steps 4 through 9 if you had used n rather than n – 1?

Answer 1

Claim:smashed group has higher speed than hit group

Null and alternate hypothesis

H0:

H1:

The level of risk that means level of significance we take 5%

We use t test for two independent samples

Since =0.05

Degree of freedom = 38

t critical value =

Test statistics:

N1: 20
df1 = N - 1 = 20 - 1 = 19
M1: 27.6
SS1: 1024.8
s21 = SS1/(N - 1) = 1024.8/(20-1) = 53.94


For smashed group

​​​​

N2: 20
df2 = N - 1 = 20 - 1 = 19
M2: 41.55
SS2: 838.95
s22 = SS2/(N - 1) = 838.95/(20-1) = 44.16


T-value Calculation

s2p = ((df1/(df1 + df2)) * s21) + ((df2/(df2 + df2)) * s22) = ((19/38) * 53.94) + ((19/38) * 44.16) = 49.05

s2M1 = s2p/N1 = 49.05/20 = 2.45
s2M2 = s2p/N2 = 49.05/20 = 2.45

t = (M1 - M2)/√(s2M1 + s2M2) = -13.95/√4.9 = -6.3

Rejection region

R= {t:t<-1.686}

Decision

Since t=-6.3 <-1.6 so we rehte the null hypothesis .

So there sufficient evidence to conclude that the smashed group has higher speed than hit group.