PSY 310: Exam #3
t or f The t statistic uses the sample variance in place of the population variance.
true
A repeated-measures experiment and a matched-subjects experiment each produce a t statistic with df = 10. How many individuals participated in each study?
11 for repeated and 22 for matched
If an independent-measures design is being used to compare two treatment conditions, then how many different groups of participants would be needed and how many scores would there be for each participant?
2 groups, 1 score each
A repeated-measures study uses a total of n = 10 participants to compare two treatment conditions. How many scores are measured in this study, and how many scores are actually used to compute the sample mean and the sample variance?
20 measured and 10 used
In general, what characteristics of the difference scores are most likely to produce a significant t statistic for the repeated-measures hypothesis test?
A large number of scores and a small variance
Which set of characteristics will produce the smallest value for the estimated standard error?
A large sample size and a small sample variance
If other factors are held constant, how does sample size influence the likelihood of rejecting the null hypothesis and measures of effect size such as r2 and Cohen's d?
A larger sample increases the likelihood but has little influence on measures of effect size.
A research study produces a t statistic with df = 14. For this study, which of the following designs would require a total of 30 participants?
A matched-subjects design
If a repeated-measures study shows a significant difference between two treatments with α = .01, then what can you conclude about measures of effect size?
A significant effect does not necessarily mean that the effect size will be large.
What is indicated by a large variance for a sample of difference scores?
An inconsistent treatment effect and a low likelihood of a significant difference
In general, what is the effect of an increase in the variance for the sample of difference scores?
An increase in the standard error and a decrease in the value of t
A researcher obtains t = 2.25 for a repeated-measures study using a sample of n = 10 participants. Based on this t value, what is the correct decision for a two-tailed test?
Fail to reject the null hypothesis with both α = .05 and α = .01
An independent-measures research study uses two samples, each with n = 10 participants. If the data produce a t statistic of t = 2.095, which of the following is the correct decision for a two-tailed hypothesis test?
Fail to reject the null hypothesis with either α = .05 or α = .01
Under what circumstances can a very small treatment effect be statistically significant?
If the sample size big and the sample variance is small
Which combination of factors would definitely increase the width of a confidence interval? -Decrease the sample mean and increase the sample size -Increase the sample mean and increase the percentage of confidence
Increase the sample mean and increase the percentage of confidence
Assuming that other factors are held constant, which of the following would tend to increase the likelihood of rejecting the null hypothesis?
Increase the sample mean difference
A researcher selects a sample from a population with μ = 30 and uses the sample to evaluate the effect of a treatment. After treatment, the sample has a mean of M = 32 and a variance of s2 = 6. If Cohen's d is used to measure the size of the treatment effect, which of the following would have no effect on the value of Cohen's d?
Increase the sample size
When n is small (less than 30), how does the shape of the t distribution compare to the normal distribution?
It is flatter and more spread out than the normal distribution.
Which of the following describes what a confidence interval does? -It uses a sample mean to estimate the corresponding population mean. -It uses a population mean to predict a sample mean.
It uses a sample mean to estimate the corresponding population mean.
In general, if the variance of the difference scores increases, what will happen to the value of the t statistic?
It will decrease in magnitude (move toward 0 at the center of the distribution).
If other factors are held constant, how does sample variance influence the likelihood of rejecting the null hypothesis and measures of effect size such as r2 and Cohen's d?
Larger sample variance decreases both the likelihood and measures of effect size.
Why are t statistics more variable than z-scores?
The extra variability is caused by variations in the sample variance.
Two samples from the same population both have n = 10 scores with M = 45. If the t statistic is computed for each sample, then what is the relationship between the two t values?
The sample with the smaller variance will produce the larger t statistic.
A researcher is using a repeated-measures study to evaluate the difference between two treatments. If the difference between the treatments is consistent from one participant to another, then the data should produce ______.
a small variance for the difference scores and a small standard error
For the repeated-measures t statistic, df = _____.
n - 1
Which of the following samples will have the smallest value for the estimated standard error? -n = 4 with s2 = 16 -n = 16 with s2 = 64 -n = 4 with s2 = 64 - n = 16 with s2 = 16
n = 16 with s2 = 16
If a sample of n = 16 scores is being used to make an 80% confidence interval estimate of the population mean, μ, what value(s) of t should be used?
t = ±1.341
Which of the following is the correct null hypothesis for a repeated-measures t test? -MD = 0 - µD = 0
µD = 0
Which of the following is the correct null hypothesis for an independent-measures t test?
μ1 - μ2 = 0
A repeated-measures study using a sample of n = 20 participants would produce a t statistic with df = ____.
19
A researcher reports t(22) = 5.30, p < .01 for an independent-measures experiment. How many individuals participated in the entire experiment?
24
An independent-measures study uses n = 15 participants in each group to compare two treatment conditions. What is the df value for the t statistic for this study?
28
An independent-measures research study uses a total of 40 participants to compare two treatment conditions. What is the df value for the t statistic for this study?
38
Which of the following research situations would be most likely to use an independent-measures design? -Compare the mathematics skills for 9th-grade boys versus 9th-grade girls. -Examine the long-term effectiveness of a stop-smoking treatment by interviewing subjects 2 months and 6 months after the treatment ends.
Compare the mathematics skills for 9th-grade boys versus 9th-grade girls.
