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One-Way BG ANOVA

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

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  1. One-Way BG ANOVA Andrew Ainsworth Psy 420 Obtained from www.csun.edu/~ata20315/psy420/One-Way%20BG%20ANOVA.ppt

  2. Effect Size • 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?

  3. Effect Size • 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

  4. Effect Size • Standardized Effect Size • Expresses raw mean differences in standard deviation units • Usually referred to as Cohen’s d

  5. Effect Size • Standardized Effect Size • Cohen established effect size categories • .2 = small effect • .5 = moderate effect • .8 = large effect

  6. Effect Size • Percent of Overlap • There are many effect size measures that indicate the amount of total variance that is accounted for by the effect

  7. Effect Size • Percent of Overlap • Eta Squared • simply a descriptive statistic • Often overestimates the degree of overlap in the population

  8. Effect Size • 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

  9. Our Example EPRS8540 • Eta Squared • Small .01 • Medium .06 • Large .14 Cohen (1977) • Omega Squared • Small < .06 • Medium .06 - .15 • Large > .15 Cohen (1977)

  10. Our Example EPRS8540 • There was no significant price difference among the three store types (F2, 9 = 3.12, P > .05, ).

  11. References • 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.

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