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effect size
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POMP scores vs standardized mean differences: when is POMP a sound way to combine scales?
What POMP scores are, how they differ from a standardized mean difference such as Cohen's d, when each misleads, and how to report POMP in APA style.
Read the answer →Can you run a chi-square test on weighted survey estimates?
A chi-square test on weighted survey totals treats millions of estimated people as real observations. Why that fails and what to do instead.
Read the answer →Why can a CI for Cohen's d include zero when the t test is significant?
Why an effect size interval for Cohen's d can cross zero while the mean difference interval does not, and which d and interval agree with the test.
Read the answer →Confidence interval for eta squared: does the Fisher z shortcut work?
Why the Fisher z shortcut gives unreliable intervals for eta squared, and how to get an exact one from F and its degrees of freedom.
Read the answer →Mann-Whitney effect size: is z/√N right, and which CI should you report?
Why z/√N is a shaky effect size for Mann-Whitney, why Fisher's z interval does not suit it, and which effect sizes and intervals to report instead.
Read the answer →What should you do after rejecting the null hypothesis?
A significant result is a starting point, not a conclusion. Estimate the effect, check that it is robust, and replicate before you treat it as established.
Read the answer →Why does almost everything become statistically significant with a large sample?
Large samples do not bias a test toward rejecting a true null; they detect tiny real differences. How to tell significant from important.
Read the answer →What does r mean when it is reported next to a t test, and how do you turn it into d?
Why papers report an r with a t test, how it is computed from t, what r squared means, how to convert r to Cohen's d, and how to report it in APA style.
Read the answer →How do you interpret Cohen's d, and are 0.2, 0.5 and 0.8 a real standard?
What Cohen's d says about group overlap, where the 0.2/0.5/0.8 cutoffs come from, why fields differ, and how to report d in APA style.
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