Stats - Quick Review

2. What is the measure of how much readings in a sample vary from the mean called? How do you calculate it? Why is it useful? The measure of how much readings in a sample vary from the mean is called standard deviation. In order to calculate standard deviation, you need the equation:

Or you can follow these steps: 1. Calculate the mean (x) 2. Measure the deviations (x-x) 3. Square the deviations (x-x)2 4. Add the squared deviations (x-x)2 5. Divide by the number of samples (n) Standard deviation is useful because it tells us how spread out are the readings; hence, this will give you a better picture of the data than just the mean alone (i.e. by using standard deviation we have a ‘standard’ way of knowing which data is normal and which is not).