PY 211 Exam 3

What is the main difference between a Z score and a t score?

We use t scores when the population variance is unknown.

In what type of test do we use difference scores?

t-test for dependent means

How can we make a t distribution more closely resemble a normal curve?

increase the sample size

What changes in the equation when we estimate the population variance from the scores in the sample?

Dividing the sum of squared deviations by N-1 instead of N

In a t test for dependent means, the population mean (uM) always equals...?

Population means is always 0 in a t test for dependent means

What is the comparison distribution for a t test of independent means?

Distribution of difference between means

What does it mean if you conducted a t test for independent means and found the t score equaled 0?

the two sample means must be equal

A sample is made up of the following scores: 10, 12, 15, 16, and 23. What is the estimated population variance? What degrees of freedom did you use in the formula?

estimated population variance= 24.7
df= 4

In calculating a t test, if there were 16 participants and the research is using the 5% level of significance, what would be the cutoff t score?

READ THE T TABLE****
df= 15; .05; cutoff= 1.753

What do we compare using a t test for dependent means?

A sample in which participants each have two scores, e.g., pre/post test scores

What do the values in "t (34) = 7.96, p < .05" represent?

34 = degrees of freedom (35 participants)
7.96 = calculated t value was significant given the alpha set at .05

In a t test for independent means, what does it mean when we reject the null hypothesis?

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

What is the mean of a distribution of differences?

mean of a distribution of differences is always 0

In t tests, when do we reject the null hypothesis?

If the compared t test is more extreme than the cutoff score

What happens if we run several t tests using the same samples?

the chance of one of the t tests being significant will be greater than 5% (assuming we set the alpha at .05)

How does an analysis of variance (ANOVA) differ from a t test for independent means?

ANOVA can be used to compare 3 or more groups; t test for independent means cannot be used to compare 3 or more groups

What does it mean if the null hypothesis is true in an ANOVA?

if the null is true in an ANOVA, there is less variance among the means of the samples than if the null were not true

What is the denominator in an F ratio for a planned comparison?

The denominator a F ratio for a planned comparison is the overall within-groups population variance estimate, regardless of the groups being compared

What would the numerator in an F ratio for a planned comparison depend on?

Which pair of means is being compared

If we are going to reject the null hypothesis based on statistically significant F ratio, what would expect the F ratio to be, generally?

The F ratio would be much larger than 1

In an analysis of variance with a within-groups variance estimate of 2.5 and a between-groups variance estimate of 14.4, what is the F ratio? ***

5.76

If you have an estimated population variances for 4 groups that are: 12, 19, 25, and 28, what is the within-groups estimate of the population variance?

21

What procedure would we use to keep the alpha at .05 for planned contrasts?

Bonferroni

What are the conventions for effect size using ANOVAs, R2?

small: .01
medium: .06
large: .14

If we know an ANOVA (F) with three groups is significant, what is the most accurate conclusion?

The 3 groups do not all come from population with the same mean. However, is it not clear which population

What do the values in "F (3, 56) = 8.23, p < .05" represent?
A. What does (3, 56) represent?

dfbetween and dfwithin

What do the values in "F (3, 56) = 8.23, p < .05" represent?
B. How many groups were there in this study?

4 (dfbetween + 1)

What do the values in "F (3, 56) = 8.23, p < .05" represent?
C. How many participants were in this study?

60 (subtracted on for every group)

What do the values in "F (3, 56) = 8.23, p < .05" represent?
D. What is the calculated F score?

8.23

What do the values in "F (3, 56) = 8.23, p < .05" represent?
E. Where was the significance level (alpha) set?

.05

How many cells would there be in a 2x2 study?

4 cells

What is an interaction effect?

occurs when the influence of one variable that divides the groups changes according to the level of the other variable that divides the groups

How many F ratios would be calculated in a two-way analysis of variance?

three, 2 main effects for each of the 2 variables & 1 for the interaction effect

What analogy describes how a repeated measures ANOVA relates to an ordinary ANOVA?

A repeated measures ANOVA is to an ordinary ANOVA the same as a t test for dependent means is to a t test of independent means due to the pre/post test nature of the data

What does it mean to dichotomize a variable?

Dividing variables into two groups: one group is high on the variable, the order is low on the variables (ex: age, younger, older)