How it works
The mean is the sum of the values divided by how many there are. The median is the middle value once the list is sorted (or the average of the two middle values when the count is even). The mode is the value that appears most often, and the range is the largest value minus the smallest.
The mean uses every value, so a single very large or small number can pull it a long way. The median only depends on order, which makes it the better summary for skewed data such as incomes or home prices.
A list can have more than one mode (bimodal or multimodal) or none at all if every value appears exactly once.
Formula
Mean = Σx ÷ n · Median = middle value of the sorted list · Range = max − min
Questions people ask
When should I use the median instead of the mean?
Use the median when the data is skewed or has outliers. For example, a few very high salaries raise the mean salary a lot but barely move the median.
Can a data set have more than one mode?
Yes. If two or more values tie for the highest count, all of them are modes. If every value appears once, there is no mode.
How is the median found for an even number of values?
Sort the list and average the two middle values. For 2, 5, 7, 10 the median is (5 + 7) ÷ 2 = 6.