Stats

Question 1

Latin square

Answer 1

Counterbalancing is used to control order effects that may occur when a within-subjects design is used – i.e., when subjects in each group will receive or participate in all levels of the independent variable. The Latin square is a type of counterbalanced design that ensures that the different levels of the independent variable are assigned to the groups of subjects so that each level appears an equal number of times in each ordinal position.

Question 2

The Solomon four-group design is used to control which of the following threats to a study’s internal validity?

A. history

B. statistical regression

C. pretest sensitization

D. differential selection

Answer 2

C is correct. Pretest sensitization is also known as testing and threatens a study’s internal validity whenever taking a pretest systematically affects subjects’ performance on the posttest. When using the Solomon four-group design, the effects of taking a pretest can be assessed which helps determine if an apparent effect of the independent variable on the dependent variable is actually due to the independent variable rather than the pretest.

Question 3

Factorial ANOVA

Answer 3

A factorial ANOVA is used when a study has more than one independent variable. Factorial designs also allow for the assessment of both main effects (the effects of each independent variable considered individually) and interaction effects (the effects of each variable at the different levels of the other variable). The study described in this question has two “significant main effects” for the independent variables: type of reading program and past level of reading comprehension. And a “significant interaction effect” means that the effects of the different reading programs varied significantly for students at different reading levels. For example, “Reading Program A” may have been highly effective for above average students, moderately effective for average students, yet ineffective for below average students. On the other hand, “Reading Program B” may have been only effective for below average students, while “Reading Program C” may not have been effective for any students.

Question 4

A teacher administers a math achievement test to the 25 students in her 6th grade class on the first day of the semester and then again on the last day of the semester to see how much they gained in math ability. To analyze the data she obtains, the teacher should use which of the following statistical tests?
Select one:
A. t-test for a single sample
B. t-test for correlated samples
C. t-test for uncorrelated samples
D. t-test for multiple means

Answer 4

For the exam, you want to know when it is appropriate to use each of the t-tests listed in answers a, b, and c.
a. Incorrect The t-test for a single sample is used to compare an obtained sample mean to a known population mean.

b. CORRECT The t-test for correlated (dependent) samples is used to compare two related means – e.g., means obtained from the same sample at two different times.
c. Incorrect The t-test for uncorrelated (independent) means is used to compare two means obtained from unrelated samples

Question 5

Single-sample chi-square

Answer 5

Nominal data. One variable.

Question 6

A Reliable Change Index (RCI)

Answer 6

computed by dividing the difference between the pretreatment and posttreatment scores by the standard error of the difference between the two scores. If the RCI is greater than 1.96, then the difference is reliable, a change of that magnitude would not be expected due to the unreliability of the measure.