These are ways to characterize a population or a sample. The mean is the average score. It is calculated by dividing the sum of scores by the number of scores. For example, the average of the series {4, 7, 8, 9, 9} equals 7.4, (4 7 8 9 9 divided by 5). The median refers to the number that falls in the middle of the sample; half of the scores lie above it and half lie below. In this case the median is 8. The mode refers to the most common score. In this case the mode is 9. Each measure of central tendency has different advantages and disadvantages.