Chapter 5 tTests Measuring the Differences Between Group
Chapter 5 t-Tests: Measuring the Differences Between Group Means
t-test o Comparing group means o What is the probability of getting a difference this large by chance alone?
t-test o Type of Data Required o Nominal-level independent variable with two levels o Continuous dependent variable
t-test o Assumptions o Two mutually exclusive groups o Normally distributed dependent variable o Homogeneity of variance
Example from Literature
t-tests o Formulas o Pooled or equal variance o Separate or unequal variance o Correlated or paired
t-test o Alpha level o Power n One vs. two-tailed o Effect size o Sample size
Cohen’s Effect Sizes - t-test o Small o Moderate o Large =. 2 =. 5 =. 8
Effect sizes o GRE Scores n n Mean = 500 Standard Deviation = 100
Effect sizes o LOPSS n n Difference between groups = 17 points Standard deviation = 24
Exercises o 1. Do individuals who have never smoked differ from those who are still smoking on the following two measures: confidence during stressful situations and life purpose and satisfaction? o 2. Do current ratings of satisfaction with weight differ significantly from ratings of weight at age 18?
SPSS - t-test, 2 groups o ANALYZE n Compare Means p Independent Samples T Test
SPSS - t-test, one group measured twice o ANALYZE n Compare Means p Paired Samples T Test
- Slides: 13
