Measures of central location: the measure of central location reflects the locations of all the actual data points, the arithmetic mean or average is the most popular and useful measure of central location. Mean= sum of observations/number of observations: affected by extreme values (outliers, appropriate for describing interval data, ex. Heights of people, grades of papers: ex. Weighted mean: weighted mean is a method of computing a type of arithmetic mean of a set of numbers in which some elements of the set carry more importance (weight) than others, ex. Final mark is made up of: quiz 10%, test 30%, exam. Weighted mean= sum of (weight * x)/ sum of weight: ex. Mean salary= sum of (# of employees * salary)/ sum of employees: ex. Moose per km2, no weight, given # of moose and area of park: sum of moose/sum of area. Grouped data mean= sum of (frequency * midpoint)/ sum of frequencies.