What is Standard Deviation and Percent Standard Deviation?

If you’re in an advanced chemistry or college chemistry course you’re probably going to be asked to calculate the standard deviation of your results for a lab. It’s called a lot of things, but most usually either standard deviation or relative standard deviation. Here’s how to calculate it:

[Calculation]
SD or RSD = the square root of ((sum of (mean or average – value) / number of values – 1)

Then some professors or TAs will ask for the percent standard deviation or the percent relative standard deviation. The way to calculate the percent standard deviation is:

[Calculation]
Standard Deviation Value / mean or average value x 100

Hope this helps clear things up.

[Image Credit] Chad Miller

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