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

you mean 68.25% and 95.45% confidence limits
68.25% confidence limits is the average value +/- one standard deviation
95.45% confidence limits is the average value +/- two standard deviations


say for data in cells G2 to G18

Place the following in an unused cell. Lets say G19
=AVERAGE(G2:G18)
Place the following in an unused cell Lest say G20
=STDEV(G2:G18)

68.25% confidence limits
=G19+G20
and
=G19-G20

95.45% confidence limits
=G19+G20*2
and
=G19-G20*2

Note: Multiplication is performed before addition

STDEV
Estimates standard deviation based on a sample. The standard deviation is a measure of how widely values are dispersed from the average value (the mean).

Syntax
STDEV(number1,number2,...)

Number1, number2, ... are 1 to 30 number arguments corresponding to a sample of a population. You can also use a single array or a reference to an array instead of arguments separated by commas.