Determining 2.5% and 95% confidence limits using Excel?

Question

I have some data; namely multiple results from blood analyses (eg 100 plasma sodiums). I need to work out the reference ranges from a distribution curve. Can you use MS excel to do this? I can't seem to find it in data analysis.

Answer 1

Sure, type =stdev(range_of_cells) the same way you use =sum(range_of_cells); this gives you a standard deviation. This gives you a 68.2% confidence level, to get 95% confidence, multiply this standard deviation by 2 (most people multiply by 2 but I think officially 1.96 is more accurate). I have never heard of a 2.5% confidence limit, does this mean you would only be 2.5% confident your answer is right?