# Standard deviaion watch

1. can somebody please explain how to do standard deviation for a non maths alevel taking biology student?
2. Standard deviation is a measure of how spread out your results are.

The standard deviation equals the square root of variation.

Variation = The mean of the squares minus the square of the mean.
May seem confusing but it isn't. The mean of the squares means, square all your values, and find the mean (so add them all up and divide by how many there are). And then you minus from this the square of the mean of your normal data.

And once you have the variation, you square root it to get the standard deviation.

Quick example:
Data - 3,4,5,6

Variation = (3^2 + 4^2 + 5^2 + 6^2)/4 - ((3+4+5+6)/4)^2
= 21.5 - (4.5)^2 = 21.5 - 20.25 = 1.25

Standard deviation = square root of 1.25 = 1.11

Which roughly makes sense, +- 1.11 from the median value roughly gives us the highest and lowest value, though it's measuring the variation between the data overall and not from the middle to the lowest/highest, so if we had one really high value and ten values close together, the standard deviation would be quite low.
3. Sorry, what android said is perfect, one small thing though. Here is for formula for it
4. Every exam paper I've seen has basic steps outlined for you anyway, and it's just a basic "putting numbers into your calculator" thing, as they cant really expect you to know how to do that.
5. (Original post by charllysaur)
Every exam paper I've seen has basic steps outlined for you anyway, and it's just a basic "putting numbers into your calculator" thing, as they cant really expect you to know how to do that.
AS Biology AQA unit 3X
http://store.aqa.org.uk/qual/gce/pdf...X-W-SQP-07.PDF
They do not give you the formula for standard deviation

I agree with you, although to be fair its not really that difficult, plus most calculators do it for you anyway.
6. Thank you guys, it makes so much sense now
7. Another formula you could use is:
root( Sumxsquared/n - meansquared )

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