Can you specify the study design in  your project for microRNA data? Do you know the parameters from the microRNA data results? You indicated after radiotherapy. Are you intending to calcualte sample size for before and after radiotherapy in comparison to a group that did not receive the radiotherapy? Then, it is the effect size and sample size estimates calculation for two groups' data. In addition, depending on the disease populations (a specific type of cancer and staging of cancer), some relevant and important confounding variables that affect the results of radiotherapy may need to be considered (in literature or your team's data, potentially includes social determinants data).

Dear Pamela Shiao

I would like to compare the radiation induced expression changes in blood samples collected before and after radiotherapy. I am not really going to compare the expression changes of the radiotherapy patients with an individuals did not receive radiotherapy. The expression changes of several miRNAs using Realtime PCR in the literature was expressed as fold change after radiotherapy with sample size of around 8 to 20. 

Thanks for your Answer

Here is the basics to do power analysis to estimate your sample size, you have to write your hypothesis, and based on that you decide what statistical test you will use. It should be one of the inferential statistics. so you need to determine the following: alpha {standard to be .05}, power [standard to be .80], effect size {small, moderate, or large, each test has its own value, you can find these values in the net}. Then download free programs to calculate the sample size such as G. power.

To do power analysis to estimate your sample size, you have to write your hypothesis, and based on that you decide what statistical test you will use. It should be one of the inferential statistics. so you need to determine the following: alpha {standard to be .05}, power [standard to be .80], effect size {small, moderate, or large, each test has its own value, you can find these values in the net}. Then download free programs to calculate the sample size such as G. power.

if you you still need any further help, just send me a message

Dear Muayyad Ahmad

Thank you for explanation regarding sample size. Sure i will message if i need further clarification.