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T Tests for Independent and Related Samples: 6 problems

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t Tests for Independent and Related Samples

Problem Set 2: Chapter 10 & 11: problems:

Chapter 10:

2. Describe what is measured by the estimated standard error in the bottom of the independent -measures t-statistic.
18. In 1974, Lotus 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 filmed of an automobile accident and then were asked about what they saw. One group was asked, questions 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 expect the verb was changed to hit" instead of 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

24. A researcher conducts an independent -measures research study and obtains t =2.070 with df = 28.
a. How many individuals participated in the entire research study?
b. Using a two-tailed test with α = .05, is there a significant difference between the two treatment conditions?
c. Compute r2 to measure the percentage of the variance accounted for by the treatment effect.

Chapter 11:
2. Participants enter a research study with unique characteristics that produce different scores from one person to another. For an independent -measure study, this individual difference can cause problems. Briefly explain how these problems are eliminated or reduced with a repeated -measure study.

4. A researcher conducts an experiment comparing two treatment conditions and obtains data with 10 scores for each treatment condition.
a. If the researcher used an independent-measure design how many subjects participated in the experiment?
b. if the researcher used a repeated-measures design, how many subjects participated in the experiment?
c. If the researcher used a matched -subjects design, how many subjects participated in the experiment?

10. Research has shown that losing even night's sleep can have a significant effect on performance of complex tasks such as problem solving (Linde & Bergstroem, 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 on 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 s2 = 64 for the difference scores.
a. Do the data indicate a significant change in problem -solving ability? Use a tailed test with α = .05.
b. Compute an estimated Cohen's d to measure the size of the effect.

22. In a Preview of a chapter, there is a discussion discussed as a report describing the Olympic and how marksmen can be affected by heartbeats. Pelton (1983) reported that Olympic -level marksmen shoot much better if they fire between heartbeats rather than squeezing 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 serious 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 α = .05.

Participants During heartbeats Between heartbeats
A 93 98
B 90 94
C 95 96
D 92 91
E 95 97


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