Part IV Significantly Different: Using Inferential Statistics Chapter 11    t(ea) for Two: Tests Between the Means of Different Groups

What you will learn in Chapter 11 When to use a t test How to compute the observed t value Interpreting the t value and what it means

t Test for Independent Samples Determining the correct statistic

Computing the Test Statistic Numerator is the difference between the means Denominator is the amount of variation within and between each of the two groups

Degrees of Freedom The degrees of freedom approximates the sample size Degrees of freedom can vary based on the test statistic selected For this procedure… n1 – 1 + n2 – 2

So How Do I Interpret… t (58) = -.14, p > .05 t represents the test statistic used 58 is the number of degrees of freedom -.14 is the obtained value (from the formula) p > .05 indicates the probability

Special Effects… Effect size is a measure of how different two groups are from one another Standardized difference between two group means Jacob Cohen

Computing Effect Size Small = 0.0 - .20 Medium = .20 - .50 Large = .50 and above

Effect Size Calculator http://web.uccs.edu/lbecker/Psy590/escalc3.ht m

Using the Computer Computing a t Test using SPSS

SPSS Output What does it all mean?

Glossary Terms to Know Degrees of freedom t Test Effect size Independent t Test Obtained value Critical value Effect size

Part IV Significantly Different: Using Inferential Statistics Chapter 12    t(ea) for Two (Again): Tests Between the Means of Related Groups

What you will learn in Chapter 12 When to use a t test for dependent means How to compute the observed t value Interpreting the t value and what it means

t Test for Dependent Samples Determining the correct statistic

Computing the Test Statistic Numerator reflects the sum of the differences between two groups

Degrees of Freedom The degrees of freedom approximates the sample size Degrees of freedom can vary based on the test statistic selected For this procedure… n – 1 (where n is the number of observations)

So How Do I Interpret… t (24) = 2.45, p > .05 t represents the test statistic used 24 is the number of degrees of freedom 2.45 is the obtained value (from the formula) p > .05 indicates the probability

Using the Computer SPSS and Paired Samples t Test

SPSS Output What does it all mean?