Stats Ch. 11-12 Study Practice

What are Between Groups comparisons?

Between groups are comparisons between different factors or groups in a sample. Ex. Difference between Pies and Cakes.

What are Within Groups comparisons?

Within groups are comparisons that happen within a group. Ex. Differences between pies in the pie group.

When do you use a independent samples t-test?

When comparing two groups, where each group is sampled once.

When do you use a dependent samples t-test?

When comparing one group, where the same group is retested.

What are pros of using a within groups sample?

Less participants needed to get the same df/power and participants serve as their own control group.

What are the cons of using a within groups sample?

Order/learning effects, not always feasible, and increases the potential for alternative explanations.

What are the pros of using between group samples?

No practice, order, or fatigue acting as a third variable, no “contamination” because the groups are separate, easier logistics, can study irreversible effects such as learning or surgery.

What are the cons of using between groups samples?

More participants needed more cost, time, etc.), more internal deviation, random assignment must be done carefully, and higher variability leads to lower statistical power.

Within Groups Samples =

Dependent Samples

Between Groups Samples =

independent Samples

What are Degrees of Freedom?

The number of values in a calculation that are free to vary.

What determines the degrees of freedom for your sample?

The n value (sample size) and whether we are using a between groups/independent sample (n-2=df) or within groups/dependent sample (n-1=df)

Dependent/Within-Groups: n=30 df=?

30-1=29

Independent/Between-Groups: n=30 df=?

30-2=28

Statistical Power

The probability of a test to correctly reject the null hypothesis