Lab 4

Psy 521/621

Lab 4 Activities

Learning Objectives:
    • Learn to conduct and interpret the t-test for dependent samples
    • Learn to conduct and interpret the t-test for independent samples

To accomplish these learning objectives, we will focus on the end-of-lesson exercises in Lessons 23 and 24 of the Green and Salkind book.

T-test for dependent samples (AKA, the paired-sample t-test)

DATA FILE: Lesson 23 Exercise File 1.sav

Exercise 1 (excerpted from Green & Salkind Lesson 23)

Mike wants to know if overall life stress increases or decreases as working women get older. He obtains scores on the Index of Life Stress (ILS) from a group of 100 working women when they are 40 years old, and he gets ILS scores again from 45 of these women when they are 60 years old. The ILS consists of two scores, interpersonal life stress and occupational life stress. The two scores combine to form an index of overall life stress. The SPSS file contains 45 cases, one for each woman, and four variables: interpersonal stress at 40, occupational stress at 40, interpersonal stress at 60, and occupational stress at 60.

1. Compute scores to obtain a total ILS at age 40 and age 60.
Transform(compute. Target variable = ILS_40. Numeric expression = inter_40 + occup_40. OK.
Transform(compute. Target variable = ILS_60. Numeric expression = inter_60 + occup_60. OK.

2. Compute a paired-samples t-test to determine whether overall life stress changes with age.
Click Analyze( Compare Means(Paired-Samples T Test.
Click ILS_40 and ILS_40 will appear as Variable 1 in Current Selections. Hold down the   ctrl button and click ILS_60 and ILS_60. It will appear as Variable 2 in Current Selections. Both variables should be highlighted in the box above.
Click ► and “ILS_40-ILS_60” will appear in the Paired Variables box. Click OK.

NOTE: If a participant is missing data for either variable, SPSS will not include them in the analysis.