psych stats exam 3 study guide

Ann conducts a study, and finds that the estimated population variances for the groups are 12.8, 16.3, 15.1, and 19.9. What is the within-groups estimate of the population variance?

(12.8 + 16.3 + 15.1 + 19.9) / 4 = 16.03

A school psychologist is using a depression inventory—on which a score of 0 indicates no depression and a score of 10 indicates severe depression—to see if the level of depression in fourth graders in a particular class of 20 students differs from that of fourth graders in general at a school. The results of previous testing indicate that fourth graders at the school usually have a score of 5 on the scale, but the variation is unknown. The current sample of 20 fifth graders has a mean depression score of 4.4. If the psychologist figures S = .85, the effect size (d) is

(5 - 4.4) / .85 = 0.71

Suppose you test the effects of a drug on rats' learning by giving them 0, 10, 20, or 30 milligrams of the drug. This experiment has ______ independent variable(s) and ______ values.

1; 4

In the phrase "one-way, between-subjects ANOVA," what does "between-subjects" mean?

Each participant experiences only one of the levels of the independent variable

Which of the following is the MOST serious violation of an assumption for the t test for independent means?

The populations are dramatically skewed in opposite directions

The comparison distribution for a t test for independent means is a

distribution of differences between means

In the formula, Σ(M-GM)2/dfBetween, "GM" is the

grand mean.

The most common way for a t test for independent means to be reported in a research article is

t (45) = 3.5, p < .05

A t test for dependent means would be used to compare

the level of reading comprehension of students at the beginning and at the end of a speed-reading class.

The comparison distribution for a t test for independent means is a t distribution instead of a normal curve because

the population variance is estimated.

What is the purpose of a post hoc test?

to determine which groups are significantly different from each other

A social psychologist interested in cultural differences compared women of two ethnic groups on a Role Approval Index on which high scores indicated high degrees of approval of one's own social role. The results were as follows. - Ethnic Group A: N = 15 M = 55 S2 = 6.5 - Ethnic Group B: N = 23 M = 51 S2 = 4.5 If a t test for independent means is conducted, how many degrees of freedom will be used to locate the cutoff score in the t table?

(15 - 1) + (23 - 1) = 36

If a sample includes three individuals with scores of 4, 6, and 8, the estimated population variance is

(4 + 0 + 4) / 2 = 4

If a sample includes three individuals with scores of 2, 3, and 4, the estimated population variance is

1

A professor believes the students in a statistics class this term are more creative than most other students attending the university. A previous study found that students at the university had a mean score of 35 on a standard creativity test, and the current class has an average score of 40 on this scale with an estimated population standard deviation of 7. The standard deviation of the distribution of means is 1.63. If there were 30 students in the class and the professor wanted to test the null hypothesis described in the scenario using the 5% level of significance, the cutoff t score would be

1.699

A counseling psychologist developing a technique to reduce procrastination has students time their procrastination for a week and uses this as a pretest measure of procrastination. Students then attend a workshop in which they are instructed to do a specific warm-up exercise for studying by focusing on a pleasant activity. Students again time their procrastination for a week, and the time from this second week is the posttest measure. If the psychologist finds that the sum of squared deviations from the mean of the difference scores of the sample is 135, the estimated population variance would be

135 / 9 = 15.0

If an experimenter conducts a t test for dependent means with 10 participants and the estimated population variance of difference scores is 20, the variance of the comparison distribution is

20 / 10 = 2.0

Use this ANOVA summary table to answer the questions that follow it: Between-groups 21 | 6 | 3.50 | 4.38 Within-groups 229 | 288 | 0.80 Total 250 | 294 What is the sample size for this analysis?

294

If a research article presented the results of an analysis of variance as, "F (2, 38) = 3.60, p < .05," then how many groups were there in the study?

3

Joe conducts an analysis of variance. If he rejected the null hypothesis, the most likely F value is

3.57

In an analysis of variance with a between-groups population variance estimate of 30 and a within-groups estimate of 25, the F ratio is

30 / 25 = 1.20

Which of the following research situations is most likely to use a between-subjects design?

Evaluation of the difference in verbal skills between 2-year-old, 4-year-old, and 6-year-old boys.

The results of an analysis of variance would be reported in a research article as

F (2, 44) = 3.40, p < .05

Which statement is only true for the t test for dependent means rather than t tests in general?

Pretest-posttest experimental designs are common

*p < .05 **p < .01 Which of the following statements is most likely to be true based on the results presented? -before and after manipulation-

The hypothesis testing procedure was probably a t test for dependent means.

Which of the following statements is true about t distributions?

The larger the sample size, the more a t distribution resembles a normal curve.

In which of the following situations would a t test for independent means be conducted?

a comparison of scores of participants in a memory study where one group is assigned to learn the words in alphabetical order and another group is assigned to learn the words in order of length of the word

In an analysis of variance, if the within-groups variance estimate is about the same as the between-groups variance estimate, then

any difference between sample means is probably due to random sampling error

An analysis of variance (ANOVA) differs from a t test for independent means in that an ANOVA

can be used to compare three or more groups, while a t test for independent means cannot be used to compare more than two groups.

An analysis of variance differs from a t test for independent means in that an analysis of variance

can be used to compare three or more groups, while a t test for independent means cannot be used to compare more than two groups.

When carrying out an analysis of variance with equal sample sizes, the estimated variance of the distribution of means is converted to an estimated variance of the population of individual scores by

dividing the estimated variance of the distribution of means by the number of scores in each sample

The best way to reduce the variances in the distributions of means when conducting a t test for independent means is to

increase the size of the samples

A characteristic of an F ratio is that

it can never be less than 0

When estimating the variance of a population from the sample, the sample variance cannot be used directly because

it tends to be slightly too small—it underestimates the population variance.

The comparison distribution in a t test for dependent means is a distribution of

means of difference scores.

In an analysis of variance, you reject the null hypothesis when the F ratio is

much larger than 1

Analysis of variance should be conducted only when

population variances can be assumed to be equal.

To use a one-way, between-subjects ANOVA, the dependent variable must be

scale data (interval or ratio)

Your professor asks you to update a manuscript with the results of a t test for dependent means and provides you with the following information: there were 19 people in the study, the t score was 4.36, and the result was significant at the .01 level. The best way to present this information would be

t (18) = 4.36, p < .01

An experimenter hypothesizes that biology majors score higher than literature majors on an intelligence test. If the mean score for biology majors was 18.8 and the mean score for literature majors was 21.3, and the Sdifference was 0.9, the t score was

t = (18.8 - 21.3) (0.9) = -2.25

Based on the following results, which would be the correct use of the formula, t = (M1 - M2) / Sdifference? Sample 1: Mean = 60; Variance of the distribution of means = 2 Sample 2: Mean = 50; Variance of the distribution of means = 7

t = (60 - 50) / √(2+7)

The main difference between a Z score and a t score is that

t scores are used when the population variance is unknown.

A "distribution of differences between means" can be thought of as a distribution of

the differences obtained when a sample mean from one population is repeatedly subtracted from a sample mean from another population.

When figuring the pooled population variance estimate in a t test for independent means

the estimates based on each of the samples are averaged in such a way as to give more influence to the estimate based on more participants.

A t test for a single sample would be used to compare

the hours that "C" average students spend on Facebook each week compared with students in general.

When conducting a t test for independent means, a typical research hypothesis might be

the mean of Population 1 is greater than the mean of Population 2.

If an experimenter conducts a t test for independent means and rejects the null hypothesis, the correct interpretation is that

the mean of one sample is so far from the mean of the other sample that the samples must come from populations with different means

If a t test for dependent means is reported in a research article as "t (38) = 3.11, p < .01," then

the result is significant.

Even a very small mean difference can be statistically significant if

the sample size is big and the error variance is small

The most serious violation of an assumption for an analysis of variance occurs when

the scores between and within groups are dependent

Studies using difference scores tend to have larger effect sizes than studies using other research designs because

the standard deviation of difference scores is usually low.

If a t test for dependent means is reported in a research article as "t (16) = 2.67, p < .05," then

the t score was 2.67

A t test for independent means is reported as "t (28) = 4.21, p < .01." This means

the t score was 4.21

If a research article reports that "The mean performance scores for the Normal Sleep, Reduced Sleep, and No Sleep groups were 18.0, 16.6, and 15.6, respectively, F (2, 36) = 2.95, p < .05," the most accurate conclusion is that

the three groups do not all come from populations with the same mean, although it is not clear which population means are different

One of the assumptions for the t test for independent means is that

the variance of each of the parent populations is the same.