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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!

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    $\begingroup$ 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

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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.

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