A measure of central tendency reduces a large amount of data into a single number. Exhibit8.13 defines commonly used measures. The distinction between "mean" and "weighted mean" is important. If only company averages are reported in the survey, a mean may be calculated by adding each company's base wage and dividing by the number of companies. While use of the mean is common, it may not accurately reflect actual labor market conditions, since tha base wage of the largest employer is given the same weight as that of the smallest employer. Weighted mean is calculated by adding the base wages for all engineers in the survey and then dividing by 585. A weighted mean gives equal weight to each individual employee's wage.