Statistics - Exam 3 Questions with
Accurate Answers
Between vs. Within - Subjects Design --- which statistic to use for hypothesis
testing? correct answer Between-Subjects Design, aka independent-measures
research design = use independent-samples t test
Within-Subjects Design, aka repeated-measures research design, or other non-
independent group designs (groups are not distinct from one another) = use
related-samples t test (aka t test for correlated groups)
Define confidence interval. correct answer A confidence interval is a range of
values that estimates the unknown population mean. The confidence interval
uses the t equation, solved for the unknown mean.
*See sheet for formulas for each t-statistic
Define homogeneity of variance. Why does this assumption matter? correct
answer Requires that the two populations from which the samples are obtained
have equal variances.
Necessary to justify pooling the two sample variances and using the pooled
variance in the calculation of the t statistic.
If the assumption is violated, then the t statistic contains two questionable values.
1. The value for the population mean difference which comes from the null
hypothesis and 2. The value for the pooled variance. The problem is that you
cannot determine which of these two values is responsible for a t statistic that
, falls in the critical region. In particular, you cannot be certain that rejecting the
null hypothesis is correct when you obtain an extreme value for t,.
Describe the procedure (three steps) to compute the independent-measures t
test. correct answer 1. Find the pooled variance for the two samples.
2. Use the pooled variance to compute the estimated standard error.
3. Compute the t statistic.
Don't want confidence interval to equal what? correct answer Zero.
How do interval estimates differ from point estimates? correct answer A point
estimate is a single value and has the advantage of being very precise.
An interval estimate consists of a range of values and has the advantage of
providing greater confidence than a point estimate. (The interval estimate is less
precise, but gives more confidence. For this reason, interval estimates are usually
called confidence intervals).
How do we evaluate r2? correct answer = 0.01-0.09 - small effect
= 0.09-0.25 - medium effect
> 0.25 - large effect
Accurate Answers
Between vs. Within - Subjects Design --- which statistic to use for hypothesis
testing? correct answer Between-Subjects Design, aka independent-measures
research design = use independent-samples t test
Within-Subjects Design, aka repeated-measures research design, or other non-
independent group designs (groups are not distinct from one another) = use
related-samples t test (aka t test for correlated groups)
Define confidence interval. correct answer A confidence interval is a range of
values that estimates the unknown population mean. The confidence interval
uses the t equation, solved for the unknown mean.
*See sheet for formulas for each t-statistic
Define homogeneity of variance. Why does this assumption matter? correct
answer Requires that the two populations from which the samples are obtained
have equal variances.
Necessary to justify pooling the two sample variances and using the pooled
variance in the calculation of the t statistic.
If the assumption is violated, then the t statistic contains two questionable values.
1. The value for the population mean difference which comes from the null
hypothesis and 2. The value for the pooled variance. The problem is that you
cannot determine which of these two values is responsible for a t statistic that
, falls in the critical region. In particular, you cannot be certain that rejecting the
null hypothesis is correct when you obtain an extreme value for t,.
Describe the procedure (three steps) to compute the independent-measures t
test. correct answer 1. Find the pooled variance for the two samples.
2. Use the pooled variance to compute the estimated standard error.
3. Compute the t statistic.
Don't want confidence interval to equal what? correct answer Zero.
How do interval estimates differ from point estimates? correct answer A point
estimate is a single value and has the advantage of being very precise.
An interval estimate consists of a range of values and has the advantage of
providing greater confidence than a point estimate. (The interval estimate is less
precise, but gives more confidence. For this reason, interval estimates are usually
called confidence intervals).
How do we evaluate r2? correct answer = 0.01-0.09 - small effect
= 0.09-0.25 - medium effect
> 0.25 - large effect
