stats ch 10

"Elementary school children spent significantly more time reading the presence of a teacher than when the teacher was absent, t(7) = 2.804, p < .05 ( w squared=?4 0.46)." In this related-samples t test, how many participants were observed?

8

In a sample of 17 participants, a researcher estimates the 90% CI for a sample with a mean of = 7 and an estimated standard error for the difference scores of 2.2. What is the confidence interval at this level of confidence?

90% CI 3.2, 10.8

In a sample of 20 participants, a researcher estimates the 99% CI for a sample with a mean of = 3.7 and an estimated standard error for the difference scores of 0.2. What is the confidence interval at this level of confidence?

99% CI 3.1, 4.3

A researcher selected a sample of 24 participants and observed their behavior at two times. The result of a related-samples t test at a .05 level of significance was t = 2.68. Which of the following correctly describes the result of this test?

A related-samples t test is the correct test for this study; the result of the test is significant.

A researcher sampled 25 participants and measured their alcohol consumption (in ounces) in both a home and a bar setting. If the mean difference in satisfaction ratings for this sample was 11.4 ± 2.5 , then what is the decision at a .05 level of significance?

Alcohol consumption significantly differed, t(24) = 4.56.

To increase the value of estimated Cohen's d, a researcher increases the sample size. Will this change the value of d?

No; the sample size is not used to compute effect size.

A researcher conditions rats to fear a tone that was sounded just prior to a brief shock. To measure fear following this conditioning, she records the number of lever presses by each rat in the presence and in the absence of the tone. It was hypothesized that reduced lever pressing in the presence of the tone was evidence for a conditioned fear response in rats. If the researcher tested this hypothesis at a .05 level of significance (two-tailed test), then what is her decision if she computes t = ñ2.842 in a sample of 8 rats?

Reject the null hypothesis; there is evidence for a conditioned fear response.

A researcher sampled 16 couples and measured the mean difference in their marital satisfaction. Each couple was paired and the differences in their ratings (on a 7-point scale) were taken. If the mean difference in satisfaction ratings for this sample was 1.8 ± 2.0 , then what is the decision at a .05 level of significance?

Satisfaction ratings significantly differ, t(15) = 3.60.

All other things being equal, as the degrees of freedom increase, what happens to the critical value for a related-samples t test (or for any t test, for that matter)?

The critical value decreases.

All other things being equal, as the sample size increases, what happens to the critical value for a related-samples t test (or for any t test, for that matter)?

The critical value decreases.

Which of the following is an assumption for computing the related-samples t test?

all of these: The population being sampled from is normally distributed, The population variance of difference scores is unknown, Samples are related or matched between groups, but not within groups.

Which of the following is an advantage for selecting related samples compared to selecting independent samples in behavioral research?

all of these:. Selecting related samples can be more practical, Selecting related samples minimizes standard error,. Selecting related samples increases power.

For the related-samples t test, assuming that all other values remain constant, then as samples size increases, ______.

all of these:. the value of the test statistic increases, the power to detect an effect increases, the estimate for standard error decreases

The related-samples design can ______.

be more practical

A professor computes the mean difference in exam scores before and after a lecture as 9.0 ± 14.5 , and this difference was significant. What is the effect size for this result using estimated Cohen's d?

d = 0.62 (medium effect)

A researcher computes the mean difference in locomotion in a sample of 12 rats before and 30 min after an injection of amphetamine. Rats were placed in a box with infrared beams. The number of times rats crossed the beams was used as a measure of locomotion. The mean difference in locomotion was 6.2 ± 8.4 , and this difference was significant. What is the effect size for this result using estimated Cohen's d?

d = 0.74 (medium effect)

The test statistic for a related-samples t test makes tests concerning a single sample of ______.

difference scores

Which of the following is the denominator of the test statistic for the related-samples t test?

estimated standard error for difference scores

All other things being equal, reducing the level of significance from .05 to .01 will ______ the value of the test statistic for a related-samples t test.

have no effect on

All other things being equal, increasing the sample size will ______ the value of the test statistic for a related-samples t test

increase

The related-samples design can ______ the power to detect an effect by making the standard error ______.

increase; smaller

Each of the following is an advantage for using the related-samples design, except ______.

it increases the variability measured in a study

Which of the following identifies a large effect size for a t test?

n squared equals .25

A researcher records the level of attention among 18 students during an interactive and lecture portion of a single class. If she computes a related-samples t test at a .05 level of significance (two-tailed test), then what are the critical values for this test?

plus or minus 2.110

A researcher matched 30 participants on intelligence (hence 15 pairs of participants), and then compared differences in emotional responsiveness to two experimental stimuli between each pair. For this test, what are the critical values, assuming a two-tailed test at a .05 level of significance?

plus or minus 2.145

A researcher records the strength of a conditioned response among 12 rats in the presence and absence of conditioned cues. If he computes a related-samples t test at a .05 level of significance (two-tailed test), then what are the critical values for this test?

plus or minus 2.201

The denominator of the test statistic for a related-samples t test ______

provides an estimate of the error associated with the difference scores

A professor compares scores on a competency exam among students at two times during a single semester. What type of t test is most appropriate for this study?

related-samples t test

A researcher compares the difference in the amount of texting by students in class during the first week and last week of classes. The type of design described here is called a ______.

repeated-measures design

A type of related-samples design in which participants are observed more than one time is called a ______.

repeated-measures design

researcher records the time it takes (in seconds) for participants to respond (by pressing a key) to a familiar and an unfamiliar word flashed onto a computer screen. In this study, the difference in response time for each participant is compared. The type of design described here is called a ______.

repeated-measures design

Compared to the two-independent-sample t test, the related-samples design decreases ______

standard error

A researcher selects a sample of 24 college students and has them rate their liking for two advertisements aimed at improving the image of the college. The researcher finds that liking ratings significantly differed, t = 2.900. Use omega-squared to compute the proportion of variance for this result

w squared = .24

In a sample of 26 participants, a researcher estimates the 90% CI for a sample with a mean of = 0.6 and an estimated standard error for the difference scores of 0.1. What is the upper confidence limit for this interval?

0.77

In a sample of 26 participants, a researcher estimates the 90% CI for a sample with a mean of = 0.6 and an estimated standard error for the difference scores of 1.1. What is the upper confidence limit for this interval?

2.5

Two researchers analyze the same data set. Researcher A uses a two-independent-sample t test and decides to retain the null hypothesis. Researcher B uses a related-samples t test and decides to reject the null hypothesis. Which of the following is a likely explanation for the disparity in the decisions made?

The related-samples t test had greater power to detect the effect.

What are the degrees of freedom for the related-samples t test?

n subscript D minus 1

A researcher tests how well participants know their spouse while under hypnosis, and again without hypnosis. It was hypothesized that participant responses would be more accurate (greater number of correct responses) when under hypnosis. The mean number of correct responses was M = 5.30 under hypnosis and M = 3.40 without hypnosis in a sample of 30 participants. If the estimated standard error for difference scores was 2.52, then what is the decision at a .05 level of significance (two-tailed test)?

Retain the null hypothesis; responses were not more accurate under hypnosis.

A researcher asks a sample of brothers and sisters to rate how positive their family environment was during childhood. In this study, the differences in ratings between each brother and sister pair were compared. The type of design described here is called a ______.

matched-samples design

Which of the following is a type of related-samples design in which different participants are observed in each group, but treated statistically as if they are the same persons in each group?

matched-samples design

One difference between a repeated-measures design and a matched-samples design is that ______.

only one design involves observing the same participants in each group

A researcher measures deviant behavior in a sample of 12 children from abusive homes (Sample A). Another researcher measures the same behavior in a sample of 18 children from abusive homes (Sample B). Which sample is associated with larger degrees of freedom?

sample B

To compute a related-samples t test, a researcher has to know many values. Which of the following is not a value that the researcher must know to compute this test?

the population variance of difference scores

How does the test statistic differ for a t test using the repeated-measures versus the matched-samples design?

The test statistic for the repeated-measures and the matched-samples designs do not differ; the test statistic is computed the same.

Which type of error is used to compute the confidence interval for two related samples selected from at least one population with an unknown variance?

estimated standard error for the difference scores

A researcher selects a sample of 36 dog owners and measures their responsiveness to pictures depicting the humane and inhumane treatment of dogs. The researcher finds that responsiveness significantly differed, t = 3.243. Use eta-squared to compute the proportion of variance for this result.

n squared = 0.23

When reporting data in a results section, it is ______ necessary to identify the type of t test computed

not

A researcher conducts a study in which different participants are independently observed within groups, and the same participants are observed between groups. If there are only two groups, then what type of t test is appropriate for this study?

related-samples t test

A researcher conducts a study in which the population variance of difference scores between two groups is unknown. What type of t test is most appropriate for this study?

related-samples t test

A researcher conducts a study in which the same participants are observed across each level of the independent variable. If there are only two levels of the independent variable, then what type of t test is appropriate for this study?

related-samples t test

A researcher placed male rodents in the presence and absence of a conspecific male. Cortisol (a stress hormone) levels were compared at both times. What type of t test is most appropriate for this study?

related-samples t test

Each of the following is an estimate of error for a t test, except ______.

standard error

Using APA format, which value is typically given in parentheses when reporting the results for a t test?

the degrees of freedom

Which of the following is the numerator of the test statistic for the related-samples t test?

the mean difference observed minus the mean difference stated in a null hypothesis

Each of the following is needed to compute the estimated Cohen's d, except ______.

the standard error