Measures of central tendency show the center of a data set. Three of the most commonly used measures of central tendency are the mean, median, and mode.
Mean is another word for average. Here is the formula for computing the mean of a sample:
With this formula, you compute the sample mean by simply adding up all the elements in the sample and then dividing by the number of elements in the sample.
Here is the corresponding formula for computing the mean of a population:
Although the notation is slightly different, the procedure for computing a population mean is the same as the procedure for computing a sample mean.
Greek letters are used to describe populations, whereas Roman letters are used to describe samples.
The median of a data set is a value that divides the data into two equal halves. In other words, half of the elements of a data set are less than the median, and the remaining half are greater than the median. The procedure for computing the median is the same for both samples and populations.
The mode of a data set is the most commonly observed value in the data set. You determine the mode in the same way for a sample and a population.