Independent Samples t TestsSPSS

Read This Article

Wuensch, K. L., & Moore, C. H. (2004). Effects of physical attractiveness on evaluations of a male employee’s allegation of sexual harassment by his female employer. Journal of Social Psychology, 144, 207-217.

Download the Data

• http://core.ecu.edu/psyc/wuenschk/SPSS/Reverse-Pattr-Guilt.sav

• These data are from the research reported in the article.

• Bring the data into SPSS.

The Variables

The grouping variable is P_Attr1 indicates the plaintiff was attractive2 indicates that he was not attractive

The test variable is Guilt1 = definitely not guilty9 = definitely guilty

The Values Are Already Labeled

The Analysis

Analyze, Compare Means, Independent Samples T Test

The Group Statistics

The t Test

Download Files to Estimate Cohen’s d

• Go to http://core.ecu.edu/psyc/wuenschk/SPSS/SPSS-Programs.htm

• Download two files, .sav and .sps

Enter Values in .sav File

Enter “Equal Variances Assumed” statistics.

Run the Syntax File

Just click on RUN, ALL.

Look Back at the .sav File

Write the Summary Statement

When the plaintiff was physically attractive, the jurors were significantly more certain of her guilt (M = 6.21, s = 1.81, n = 160) than when the plaintiff was not physically attractive (M = 5.52, s = 2.17, n = 164), t(314.4) = 3.08, p = .002,d = .34, 95% CI [.12, .56].

Equal Variances Assumed or Not

• I followed Zimmerman’s advice and reported the “equal variances not assumed” t, because the sample sizes were not equal.

• But you must always use the “equal variances assumed” t and df when using the program that estimates Cohen’s d.

SD or s• For many years, “SD” was the APA-

approved symbol for standard deviation.• In the most recent Publication Manual they

added “s” as appropriate to symbolize the sample standard deviation.

• Only time will tell whether authors shift from “SD” to “s.”