Standard deviation

[Tockomtele]

I'm probably posting this in the wrong session but would anyone be able to help?

I need to calculate standard deviation for an 'experiment' I've done. I have a before and and after data of 5 people.
I'm not sure what my 'value' and mean are in this case.
I hope this makes sense to someone on here, I need to submit this thing on Monday.

I’m shite at stats but I’ll reply in the hope someone who’s not a total charlatan will be along in a minute!

Don't usually need to calculate standard deviation but my usual approach is to Google 'what I plan on doing' plus 'Excel'
Loads of tutorials out there. This one looks quite comprehensive
www.excel-easy.com/examples/standard-deviation.html

I'm assuming you have access to Excel?

How many data points do you have - just 5? It won’t really be meaningful to work out s.d. with 5 data points.

secondly, s.d. isn’t for comparing two data sets - so maybe you could work it out on the difference between the before and after data, or work it out twice (once on the ‘before’ data set and separately in the ‘after’ data) and compare.

You'll need to unpack what you're trying to do here.

You could calculate separate st devs for before and after or you could calculate the st dev of the difference between before and after. Depends what you want to find out.

Thank you all.
I know it's probably not meaningful and I have no idea why I have to do it other than I've been told I need to do a t-test and add results to get a distinction on my Access project. :-) We've not even covered anything like this, the tutor explained it but I forgot...

You can do your t-test here: https://www.graphpad.com/quickcalcs/ttest1.cfm

Assuming that it's the same people doing before and after then you need to select paired t-test.

Ok, So I measured people's concentration levels before and after drinking coffee. (well, twice, actually with different strengths).
I'll need to check if my results were statistically significant (mwhahh).
I have before and after data for 5 people. If I calculate SD before and SD after, what next? Do I average the two? (I'd need to put one SD figure into an online 'two tailed t-test'...)

Sd on a sample of 5 isn't great

You put 1 sd into the test as it assumed they are all the same perhaps ? Homogeneity

Testing to see if the difference between 2 means is significant

https://onlinestatbook.com/2/testsoffmeans/differencemeans.html

For a paired test you calculate the difference between conditions (so the difference between before and after in your case). You then calculate the mean and st dev of the differences and use those for the t-test.

Thank you all! I really appreciate it.
I'll go with what @NotDavidTennant said, that makes it look simple.