First I have to admit that my knowledge in statistics is very basic.

I'm a surgeon (that explains the reason).

I'm trying to conduct a meta-analysis for which the reported data in the articles I include must be in means and SD. I forgot to mention that I'm using RevMan 4.2 (from the Cochrane corporation) to do the calculations.

The problem is that most of the articles I included in my analysis reported their data as mean and range (not SD); example:

Duration of the operation was 165 (90-450) minutes. No SD

Is there a way to calculate the SD if I know the mean, the range and the number of datapoints?

If there is a way to do that, please let me know as soon as possible.

Thanks