Estimating Magnitude of Effect
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What is R^{2}?
 The variability accounted for by the full model
 The sum of squares for the model divided by the SS total

How might one express the magnitude of effect?
 1) Find the R^{2}
 2) Express the difference in means and SD

How might one express the difference between the means and SD of two data sets
 The means must be compared in SD units
 Cohen's D is employed

What is the formula for independent group Cohen's D?
Mean 1 mean 2 divided by the standard deviation of the scores (or residuals)

How can we estimate d values?
If population means or SD are not known we replace the parameter values with their corresponding statistics

What is a small effect size?
0.20

What is a medium effect size?
0.50

What is a large effect size?
0.80

What is the d value used for?
 As a descriptive statistic (provides an index that can be used to compare effect sizes across different experiments)
 Deciding upon sample sizes
 Estimating power

What is experimental precision?
 The amount of variability in true parameter estimates
 The less variability, the greater the precision

How can we increase experimental precision?
 Reduce the size of standard error
 The best way of doing this is to increase sample size