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# One-Way BG ANOVA - PowerPoint PPT Presentation

One-Way BG ANOVA. Andrew Ainsworth Psy 420 Obtained from www.csun.edu/~ata20315/psy420/One-Way%20BG%20 ANOVA .ppt. Effect Size. A significant effect depends: Size of the mean differences (effect) Size of the error variance Degrees of freedom Practical Significance

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### One-Way BG ANOVA

Andrew Ainsworth

Psy 420

Obtained from

www.csun.edu/~ata20315/psy420/One-Way%20BG%20ANOVA.ppt

• A significant effect depends:

• Size of the mean differences (effect)

• Size of the error variance

• Degrees of freedom

• Practical Significance

• Is the effect useful? Meaningful?

• Does the effect have any real utility?

• Raw Effect size –

• Just looking at the raw difference between the groups

• Can be illustrated as the largest group difference or smallest (depending)

• Can’t be compared across samples or experiments

• Standardized Effect Size

• Expresses raw mean differences in standard deviation units

• Usually referred to as Cohen’s d

• Standardized Effect Size

• Cohen established effect size categories

• .2 = small effect

• .5 = moderate effect

• .8 = large effect

• Percent of Overlap

• There are many effect size measures that indicate the amount of total variance that is accounted for by the effect

• Percent of Overlap

• Eta Squared

• simply a descriptive statistic

• Often overestimates the degree of overlap in the population

• Omega Squared

• This is a better estimate of the percent of overlap in the population

• Corrects for the size of error and the number of groups

• Eta Squared

• Small .01

• Medium .06

• Large .14

Cohen (1977)

• Omega Squared

• Small < .06

• Medium .06 - .15

• Large > .15

Cohen (1977)

• There was no significant price difference among the three store types (F2, 9 = 3.12, P > .05, ).

• Cohen, J. (1977). Statistical power analysis for the behavioral sciences. NY: Academic Press. Cited with regard to intepretation of omega-square.

• Cohen, J. (1988). Statistical power analysis for the behavioral sciences . Second ed., Hillsdale, NJ: Erlbaum.

• Olejnik, S., & Algina, J. (2003). Generalized eta and omega statistics: Measured for effect size for some common research designs, Psychological Methods, 8, 434 – 447.