1

PSY6010: Statistics, Psychometrics and Research Design

Professor Leora LawtonSpring 2007

Wednesdays 7-10 PMRoom 204

2

Reliability Test for Scales - Cronbach’s Alpha

Another data reduction technique, but useful when they aren’t factors (different sets of attitudes) but rather, measures of different facets of the same attitudes, as measured by a Likert Scale.

• GUI: Analyze – Scale – Reliability Analysis – Add Likert scale items into menu window. Model = alpha

• For Statistics, click on Scale, Scale if item deleted, and Means.

• Drop out any for whom, when deleted, increase the Cronbach’s alpha score.

• Create variable which is a sum of the Likert values, e.g., compute newvar = var1 + var2 + var3.

3

Experimental Design Analyses

OLS Regression – behavioral modeling• tests for relationships between the DV and IV, and if a time component is

included, can examine causality. It’s good for understanding behavior or attitudes or functioning.

• Other methods are more about predicting group membership, or determine group differences. The latter question is pertinent for experimental design research.

Experimental Design Methods: Looking for Group Differences• Logistic: Change versus no Change following intervention. • Z-tests (for proportions) on outcome variable, or T-tests (for means), or

testing for differences between two groups (e.g., control/test). See Handout.

• Go to website: http://www.dimensionresearch.com/resources/calculators/ttest.html

• ANOVA, ANCOVA, or MANOVA or MANCOVA (see text 4th edition, pg 27 Table 2.1).

4

One Dependent Variable – Analyses of variance and covariance

A. One-Way ANOVA: for example, assessment score for group 1 without training versus group 2 with training.

• DV is one continuous or interval variable.

• IV is one categorical variable

• GUI: Analyze – Compare Means – One-Way Anova

5

Multivariate Analyses of Variance

• For SPSS, use from GLM for anova-like models that feature more than a bivariate test, that is, look at multivariate tests (hence the M in Manova or Mancova for multiple dependent variables), and Factorial ANOVA and ANCOVA address multiple IVs.. . – GUI: Analyze Generalized Linear Model

Univariate (for singular dependent variable)Multivariate (for 2 or more dependent variables)

• Factorial ANOVA or t-test– DV is one continuous or interval variable.– IV is one categorical variable (your critical group identifier), but

multiple covariates allowed. • ANCOVA: For example, single DV (continuous) and

continuous IVs. • And so forth…