Can you give me three reasons for reporting effect sizes?

Your estimate of the effect size constitutes your study’s evidence. A p value might tell you the direction of an effect, but only the estimate will tell you how big it is.

Reporting the effect size facilitates the interpretation of the substantive significance of a result. Without an estimate of the effect size, no meaningful interpretation can take place.

Effect sizes can be used to quantitatively compare the results of studies done in different settings.

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One Response to Can you give me three reasons for reporting effect sizes?

Good site. A correction: p-values do not tell the direction of a result, only the probability that it or one more extreme would occur if the null hypothesis were true.

A contribution to your quotation list:

The researcher armed with a confidence interval, but deprived of the false respectability of statistical significance, must work harder to convince himself and others of the importance of his findings. This can only be good.

“The primary product of a research inquiry is one or more measures of effect size, not p values.”
~ Jacob Cohen

“Statistical significance is the least interesting thing about the results. You should describe the results in terms of measures of magnitude – not just, does a treatment affect people, but how much does it affect them.”
~ Gene Glass

Good site. A correction: p-values do not tell the direction of a result, only the probability that it or one more extreme would occur if the null hypothesis were true.

A contribution to your quotation list:

The researcher armed with a confidence interval, but deprived of the false respectability of statistical significance, must work harder to convince himself and others of the importance of his findings. This can only be good.

Michael Oakes