0
$\begingroup$

I have just had my viva and my sample size calculation was criticised as it was based on r2. I was told to base the sample size on the minimal magnitude of association. My outcome variable is HbA1c, a marker of blood glucose. The minimal magnitude of association is 6 mmol/mol. I am reporting unstandardised b. I have used mixed effects multi level models and have 15 covariates.

I am ok with accounting for clustering once i have a sample size but was wondering how i calculate the sample size? I think that i am getting confused with effect sizes.....Where would i enter my value thats considered of clinical importance? Or does this translate to the effect size? I am using GPower.

Any help would be greatly appreciated. Thank you!

$\endgroup$
0
$\begingroup$

Check out Cohen 1988 and other references that provide formulas for effect sizes defined in various ways including % variance explained (R-sq) and standardized mean differences. For an important dichotomous variable it may be easier to formulate the effect size in terms of how large the mean difference is and then translate this to % of variance explained.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.