Hi,

I came across Cohen's d statistic and I would very appreciate if anyone could provide me with a brief explanation of it and with an example rooted in a context of use.

I understand that it is equal to the difference between two sample means divided by the pooled SD. But, I am wondering what kind of information is Cohen's d actually conveying. Beside, I understand that it can be provided along with t-test. Am I right?

Any help is appreciated.

Gm

Cohen's d is a measure of effect size. Simply put it indicates the amount of different between two groups on a construct of interest in standard deviation units. It is given for two reasons:

1. It is used as a counter-point to significance tests were it gives an indication of how big or small a significant difference is. This difference can then be compared to Cohen's estimates of what is typical of a small, medium, or large effect.

2. To provide a common metric on which to compare effects for meta-analysis or what not when outcome variables may be measured on different scales.

As an example suppose we found a significant difference in self-esteem in a sample tested before an intervention and then again afterwards. A Cohen's d of .50 would suggest that the intervention program was associated with a half of one standard deviation increase in self-esteem.

and yes it can be used with t-tests.