I posted this similar question before but I didn't really clarify the values properly.

I'm trying to figure out a way to calculate the SD from these below:

Mean Pre-operation Glucose 1 = 12.2, SD =13.5

Mean Post-operation Glucose 2 = 9, SD =8.7 N= 11 people enrolled in surgery

% reduction in mean glucose = ??, SD = ??

I know calculating % reduction is easy to calculate, but how do I calculate SD?

Thanks again!

  • 1
    $\begingroup$ You can't calculate it from the information given. It depends on how pre and post are correlated. $\endgroup$
    – Glen_b
    Commented May 8, 2018 at 15:44
  • $\begingroup$ You can ascertain post- operaion percentage change in mean. And change in coefficient of variation after operation. The coefficient of variation for pre and post-operation can be computed by dividing standard deviation with mean for pre-operation and post-operation patients respectively. $\endgroup$
    – user10619
    Commented May 15, 2018 at 11:22

1 Answer 1


So this does not go unanswered here is what is basically a repeat of @Glen_b's comment. Without knowing the correlation between pre- and post-scores you cannot calculate the standard deviation. You need to ask the original authors whether they would be kind enough to do the calculations for you or share their data-set.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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