Chapter 25: Paired Samples and Blocks

AP Statistics

Paired/Matched Samples

• This situation arises when your groups are NOT independent.

• What are common situations where this occursCompare subjects with themselves before and

after treatmentCompare subjects with themselves on different

variables• NEED TO THINK!!!!!!!!!!

Logic

• If the groups are not Independent, you CANNOT use a 2-Sample Test for Means (2-Sample t-Test)

• If the groups are Paired/Matched, you are looking at the differences in the variables and that mean difference

• Since you are now only looking at one variable (difference in variables), you will perform a one-sample t-test.

Intervals and Tests

• When you groups are paired/matched, the intervals you create and the tests you perform are IDENTICAL (mostly) to the intervals you create and the tests you perform for ONE-SAMPLE T-INTERVAL and ONE-SAMPLE T-TEST

Assumptions/Conditions

Independence Assumption:Randomization Condition10% Condition

Normal Population Assumption:Need to check each group for normality. SHOW GRAPH.

Nearly Normal Condition

Paired Data Assumption Check reasonableness of this claim. BE CAREFUL

Things to remember

• It is about the differences in the variables• The null hypothesis is typically written as:

• Once you start the “mechanics” of the problem, you will be looking at things like

• You are still dealing with a t-model• Don’t use a two-sample t-test for paired data.• Don’t use a paired –t method when the data are not

paired

0:0 H

dSEd ,

Calculator HelpFor a paired t test, use the same application as for

a one-sample t-test or one-sample t-interval.