Stats Ch.9-11

One sample has a variance of s2 = 10 and a second sample has a variance of s2 = 6. Which of the following most accurately describes the pooled variance for the two samples? A. Closer to 6 than to 10 B. Closer to 10 than to 6 C. Somewhere between 6 and 10 D. Around 16

Somewhere between 6 and 10

Which of the following is a fundamental difference between the t statistic and a z-score? A. The t statistic uses the sample mean in place of the population mean. B. The t statistic uses the sample variance in place of the population variance. C. The t statistic computes the standard error by dividing the standard deviation by n - 1 instead of dividing by n. D. All of the above are differences between t and z.

The t statistic uses the sample variance in place of the population variance.

What is assumed by the homogeneity of variance assumption? A. The two samples have equal variances. B. The two sample variances are not equal. C. The two populations have equal variances. D. The two population variances are not equal

The two populations have equal variances.

With a = .05 and df = 8, the critical values for a two-tailed t test are t = ±2.306. Assuming all other factors are held constant, if the df value were increased to df = 20, what would happen to the critical values for t? A. They would increase (move farther from zero). B. They would decrease (move closer to zero). C. They would stay the same. D. Not enough information to answer

They would decrease (move closer to zero).

confidence interval

aka range of values centered around a sample statistic

A sample is selected from a population with m = 46, and a treatment is administered to the sample. After treatment, the sample mean is M = 48 with a sample variance of s2 = 16. Based on this information, what is the value of Cohen's d? Answers: A. d = 0.125 B. d = 0.25 C. d = 0.50 D. Cohen's d cannot be computed without knowing the sample size.

d = 0.50

degrees of freedom

describe the number of scores in a sample that are independent and free to vary

One sample of n = 8 scores has a variance of s2 = 6 and a second sample of n = 8 scores has s2 = 10. If the pooled variance is computed for these two samples, then the value obtained will be ______. A. closer to 6 than to 10 B. closer to 10 than to 6 C. exactly alway between 6 and 10 D. cannot be determined without more info

exactly halfway between 6 and 10

repeated measures design/ within-subject design

in which the dependent variable is measured two or more times for each individual in a single sample

d = 0.8

large effect

d = 0.5

medium effect

A researcher reports t(12) = 2.86, p < .05 for a repeated-measures research study. How many individuals participated in the study? A. n = 11 B. n = 13 C. n = 24 D. n = 25

n = 13

degrees of freedom formula (df)

n-1

Two separate samples are being used to estimate the population mean difference between two treatment conditions. Which of the following would produce the widest confidence interval? A. n1 = n2 = 10 with a pooled variance of 10 B. n1 = n2 = 10 with a pooled variance of 100 C. n1 = n2 = 20 with a pooled variance of 10 D. n1 = n2 = 20 with a pooled variance of 100

n1 = n2 = 10 with a pooled variance of 100

independent measures research design/between subjects research design

research design that uses a separate group of participants for each treatment condition

What is the sample variance and the estimated standard error for a sample of n = 9 scores with SS = 72? A. s2 = 9 and sM = 3 B. s2 = 9 and sM = 1 C. s2 = 3 and sM = 3 D. s2 = 3 and sM = 1

s2 = 9 and sM = 1

d = 0.2

small effect

With a = .01, the two-tailed critical region for a t test using a sample of n = 16 subjects would have boundaries of _______. A. t = ±2.602 B. t = ±2.583 C. t = ±2.947 D. t = ±2.921

t = ±2.947

t distribution

the complete set of t values computed for every possible random sample for a specific sample size (n) or specific degrees of freedom (df)

estimated standard error

used as an estimate of the real standard error

t-statistic

used to test hypotheses about an unknown population mean

If the null hypothesis is true, what value is expected on average for the repeated-measures t statistic? A. 0 B. 1 C. 1.96 D. t > 1.96

0

An independent-measures study comparing two treatment conditions produces a t statistic with df = 18. If the two samples are the same size, how many participants were in each of the samples? A. 9 B. 10 C. 19 D. 20

10

An independent-measures study has one sample with n = 6 and a second sample with n = 8 to compare two experimental treatments. What is the df value for the t statistic for this study? A. 7 B. 12 C. 13 D. 14

12

A repeated-measures study using a sample of n = 20 participants would produce a t statistic with df = ____. A. 9 B. 19 C. 20 D. 39

19

A researcher conducts a hypothesis test using a sample of n = 20 from an unknown population. What is the df value for the t statistic? A. 19 B. 20 C. 21 D. Cannot be determined from the info given

19

An independent-measures study with n = 6 in each sample produces a sample mean difference of 4 points and a pooled variance of 12. What is the value for the t statistic? A. 1 B. 2 C. 4√2 D. 4√8

2

What is the value of the estimated standard error for the following set of D-scores? Scores: 2, 2, 10, 2 A. 3 B. √3 C. 4 D. 2

2

A sample with a mean of M = 40 and a variance of s2 = 20 has an estimated standard error of 1 point. How many scores are in the sample? A. 4 B. 5 C. 20 D. 21

20

What is the pooled variance for the following two samples? Sample 1: n = 8 and SS = 168 Sample 2: n = 6 and SS = 120 A. 7 B. √7 C. 20.57 D. 24

24

For a repeated-measures study comparing two treatment conditions, a researcher obtains a sample of n = 9 difference scores with a mean of MD = 4 and a variance of s2 = 36. What is the value for the repeated-measures t statistic for these data? A. 4/2 B. 4/4 C. 4/6 D. 4/36

4/2

Two samples, each with n = 9 scores, produce an independent-measures t statistic of t = 2.00. If the effect size is measured using r2, what is the value of r2? A. 4/16 B. 4/20 C. 2/16 D. 2/18

4/20

A sample of difference scores has a mean of MD = 5 with a variance of s2 = 100. If effect size is measured using Cohen's d, what is the value of d? A. d = 5/10 B. d = 5/100 C. d = 25/100 D. Cannot determine without knowing the sample size

5/10

Two samples, each with n = 16 scores, produce an estimated standard error of 4 points and a t statistic of t = 2.00. What is the sample mean difference? A. 2 B. 4 C. 8 D. 16

8

For which of the following situations would a repeated-measures research design be appropriate? A. Comparing mathematical skills for girls versus boys at age 10 B. Comparing pain tolerance with and without acupuncture needles C. Comparing self-esteem for students who participate in school athletics versus those who do not D. Comparing verbal solving skills for science majors versus art majors at a college

Comparing pain tolerance with and without acupuncture needles

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? A. Reject the null hypothesis with a = .05 but not with a = .01 B. Reject the null hypothesis with either a = .05 or a = .01 C. Fail to reject the null hypothesis with either a = .05 or a = .01 D. Cannot make a decision without additional information

Fail to reject the null hypothesis with either a = .05 or a = .01

If two samples are selected from the same population, under what circumstances will the two samples have exactly the same t statistic? A. If the samples are the same size and have the same variance B. If the samples are the same size and have the same mean C. If the samples have the same mean and the same variance D. If the samples are the same size and have the same mean and the same variance

If the samples are the same size and have the same mean and the same variance

When n is small (less than 30), how does the shape of the t distribution compare to the normal distribution? A. It is almost perfectly normal. B. It is flatter and more spread out than the normal distribution. C. It is taller and narrower than the normal distribution. D. There is no consistent relationship between the t distribution and the normal distribution.

It is flatter and more spread out than the normal distribution.

Which of the following describes what a confidence interval does? A. It uses a sample mean to estimate the corresponding population mean. B. It uses a population mean to predict a sample mean. C. It uses a level of confidence to estimate a sample mean. D. It uses the sample mean to determine a level of confidence.

It uses a sample mean to estimate the corresponding population mean.