Matched Pairs t TestsSPSS

Source of the Data

Cognitive-behavioral intervention to reduce African American adolescents' risk for HIV infection

Group EC was given a standard 2-hour educational program

Group BST went through an 8 week behavioral skills training program.

The Dependent Variables

• The log-transformed frequency of condom-protected sexual intercourse

• Measured before the intervention, at posttest (8 weeks later), 6 weeks after posttest, and 12 weeks after posttest.

A Plot of the Means

Download the Data

http://core.ecu.edu/psyc/wuenschk/SPSS/MAN_1W2B.sav

Bring the data into SPSSWe want to do two matched pairs t tests

One for the EC groupOne for the BST group

Split the File by Group

Data, Split File

Conduct the Test

• Analyze, Compare Means, Paired Samples T Test, Pretest versus fu6

Obtain Estimates of Cohen’s d

• Download the .sav and .sps filesD-EqN-- Estimate Cohen's d, equal n data

(including correlated samples)d-EqN-Doc -- instructions d-EqN-Dat -- necessary data file d-EqN-Run -- syntax file

Enter Statistics Into .sav File

Run the Syntax File

Look Back at .sav File

Summary Statement, BST

• Adolescents in the behavioral skills training group (n = 20) engaged in significantly more condom-protected intercourse six weeks after the training (M = 18.80, s = 11.04) than prior to the training (M = 13.45, s = 13.77), t(19) = 2.35, p = .030, d = .43.

Summary Statement, EC

• Adolescents in the educational control group (n = 20) engaged in significantly less condom-protected intercourse at the six week followup (M = 8.60, s = 11.09) than at pretest (M = 19.8, s = 21.87), t(19) = 2.40, p = .027, d = .65.