Chapter 9: Differences among Groups SFM 651: Research Methods Dr. Johnson

T tests Between sample and mean Between independent groups Between dependent groups

Sample and mean Is a specific sample different than the mean. Degrees of freedom N-1 N is number pf participants Use a t-table to decide pg 453 If T is greater than the number shown, it is significant.

Independent T test 2 samples differ from each other Most common type of T test Degrees of freedom N1 + N2 - 2

Effect size Degree to which a treatment influenced the outcome (M1 – M2) / s M is mean S is standard deviation 0.8 or greater is large

Dependent T test Difference between 2 sets of data Degrees of Freedom – N-1

tails 1 tailed T test 2 tailed T test Can only go in one direction Can only favor one side – yes or no 2 tailed T test Can go in both directions Could favor either side

Variance True variance Error variance Portion of the difference in scores that is real Error variance Portion of the difference that is caused by participant variability

T vs R R represents the relationship between the independent and dependent variable T test can evaluate the reliability (significance) or the relationship

Analysis of Variance ANOVA ABC method Test that allows the evaluation of the null hypothesis between 2 or more groups ABC method A – square each participants score -> sum these scores B – Sum all scores -> Square the sum -> divide by number of participants C – Sum all scores in 1 -> square the sum -> divide by # participants…..same for 2….3…etc -> add all sums

Factorial ANOVA There is more than 1 independent variable The more comparisons we do, the more we can tell differences

Repeated measures ANOVA Same individual, measured at different points Throwing distance of a child over a 2 year period How do they differ Do they differ

Other types ANCOVA MANOVA Analysis of Covariance A combination of regressions and ANOVA Adjusts the dependent variable for a covariate A distractor MANOVA Multivariate Analysis of Variance More than 1 dependent variable