Hi, I am a novice research and currently putting together a proposal for research with refugee children at a centre. I do not know the number of children as I am not able to access this data due to their privacy act until my proposal is accepted. I have had some reviewer feedback asking how I determined the sample size and this is based on my guesstimate while doing volunteer work at the centre. My question is regarding some feedback I received about how I will determine power of the sample. How would I go about doing this? Is it possible when I don't actually know the population number?
Many, many thanks in advance.
Concettina,
I understand your concerns, you are being asked to perform a calculation which requires specific inputs based on information you don't have. And telling the reviewers that you used a guesstimate probably isn't going to go over well. In this case, the Resource Equation may be your friend...
It allows you to estimate what your sample sizes should be when other parameters are unknown. The formula is:
E = (the total number of experimental units) - (the number of treatment groups)
where E should be chosen to be between approximately 10 and 20
You may find the following article useful in both finding the right approach, and in justifying it to the reviewers:
https://www.einstein.yu.edu/uploadedFiles/administration/animal-care-use-committee/Lab%20Animal%20Article%20Re%20Determining%20Sample%20Size.pdf
Best of luck,
Todd
Hello, although you do not know the potential sample size, it is always possible to get some idea of minimums, so I suggest that, knowing the analyzes you will perform, and speculating on the expected minimum effect sizes, calculate the sample size to reach X statistical power given x effect size. Then you report that the minimum sample size will correspond to X, which gives a minimum statistical power X given X size of the effect.
I suggest using GPower is very simple, quite complete, versatile and free
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