gravatar for Kevin Blighe

1 hour ago by

Republic of Ireland

If we consider the Student's t-test and ignore, for now, the fact that this is RNA-sequencing (with all of its intricacies...), then it is possible to achieve 80% (0.791) Power with a 3 vs 3 comparison when:

  • we set alpha to 0.05
  • the expression of each gene has standard deviation of 1.0 in
    each group
  • the difference in mean between the TRUE differentially expressed
    genes is ⩾ 3

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Given the nature of biology, it's unlikely that we'll have any gene with that 'tight' a standard deviation; however, we can still achieve sufficient Power (0.791) with 3 vs 3 if:

  • we set alpha to 0.05
  • the expression of each gene has standard deviation of 3.0 in
    each group
  • the difference in mean between the TRUE differentially expressed
    genes is ⩾ 9

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So, this is in line with the statements made in the study to which my colleague, ATpoint, has linked. That is, with 3 vs 3, you'll only realistically be able to detect a certain percentage of the TRUE differentially expressed genes, i.e., those genes that have large effect sizes / difference in mean.

Kevin



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