Z-score is the number of standard deviations away from the mean
- Say mean is 20,
- Standard deviation is 5
- A value of 12.5 would be 1.5 z-score
- If you have the z-score and a normal distribution you can use a z-table to get the percent of area that is below the given score
If you have two different scores and you know the mean and std dev for both, you can use z-score to measure relative difference between two completely different things.
- Find the z-score, then use the chart to see what percentage of scores are below yours