10.2 Describe what is measured by the estimated standard error in the bottom of the independent measures t statistic

10.18 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.

Suppose a researcher repeats this study with a sample of today's 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

Do the results indicate a significantly higher mean for the "smashed into" group? Use a one-tailed test with a=.01.

10.22 Steven Schmidt(1994) conducted a series of experiments examining the effects of humor on memory. In one study, participants were given a mix of humorous and non humorous sentences and significantly more humorous sentences were recalled. However, Schmidt argued that the humorous sentences were not necessarily easier to remember, they were simply preferred when participants had a choice between the two types of sentences. To test this argument, he switched to an independent measures design in which one group got a set of exclusively humorous sentences and another group got a set of exclusively non humorous sentences. The following data are similar to the results from the independent measures study.

Humorous Sentences Non Humorous

4 5 2 4 6 3 5 3

6 7 6 6 3 4 2 6

2 5 4 3 4 3 4 4

3 3 5 3 5 2 6 4

Do the results indicate a significant difference in the recall of humorous versus non humorous sentences? Use a two-tailed test with a=.05.

10.24 A researcher conducts an independent measures research study and obtains t=2.070 with df=28.

1. How many individuals participated in the entire research study?
2. Using a two tailed test with a=.05, is there a significant difference between the two treatment conditions?
3. Compute r^2 to measure the percentage of variance accounted for by the treatment effect.

11.2 Participants enter a research study with unique characteristics that produce different scores from one person to another. For an independent measures study, these individual differences can cause problems. Briefly explain how these problems are eliminated or reduced with a repeated measures study.

11.4 A researcher conducts an experiment comparing two treatment conditions and obtains data with 10 scores for each treatment condition....

1. If the researcher used an independent measures design, how many subjects participated in the experiment?
2. If the researcher used a repeated measures design, how many subjects participated in the experiment?
3. If the researcher used a matched subjects design, how many subjects participated in the experiment?

11.10 Research has shown that losing even one night's sleep can have a significant effect on performance of complex tasks such as problem solving (Linde 7 Begstroem, 1992). To demonstrate this phenomenon, a sample of n=25 college students was given a problem solving task at noon on one day and again at noon the following day. The students were not permitted any sleep between the two tests. For each student, the difference between the first and second score was recorded. for this sample, the students averaged Md = 4.7 points better on the first test with a variance of s^2 = 64 for the difference scores.

1. Do the data indicate a significant change in problem solving ability? Use a two-tailed test with a=.05
2. Compute an estimated Cohen's d to measure the size of the effect.

11.22 Pelton (1983) repoerted that Olympic-level Marksmen shoot much better if they fire between heartbeats rather than sqeezing the trigger during a heartbeat. The small vibration caused by a heartbeat seems to be sufficient to affect the marksmen's aim. The following hypothetical data demonstrate this phenomenon. A sample of n=8 Olympic marksmen fire a series of rounds while a researcher records heartbeats. for each marksman, the total score is recorded for shots fired during heartbeats and for shots fired between heartbeats. Do these data indicate a significant difference? test with a=.05.

Participants During Between

Heatbeats Heartbeats

A 93 98

B 90 94

C 95 96

D 92 91

E 95 97

F 91 97

G 92 95

H 93 97

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