8.2 MEASURES OF CENTRAL TENDENCY Measures of central tendency are also called because they describe values which stand for magnitudes near the center of the distribution or around which the other values tend to cluster.
Examples:
Mean, median and mode
8.2.1 The Arithmetic Mean This is commonly known as the average. An ordinary average is one which is obtained by simply adding all the values observed, then dividing he sum by the number of values added.
WEIGHTED ARITHMETIC - Another type of average. - obtained by first multiplying each observed value by a corresponding assigned weight before summing up the products then dividing the sum of he weights.

In both instances, the arithmetic mean was computed simply by summing up then dividing the sum by the number of values added up. Symbolically, if X stands for the mean and each X¡ represents individual values to be added up to n number of variants and [∑] represents summation sign, then: 8.2.1.1 Ungrouped Data Raw data are values obtained directly either from observations or from the questionnaire results. Nothing has not yet been done to convert the data into any form, except to copy or to record them as values obtained from the direct observations.
Example:
TABLE 8.4

8.2.1.2 Grouped Data Values which have undergone some treatment, possibly in terms of arrangement into similar categories called groups or classes. To do this the following terms should be clearly understood:
Class – refers to the categories to which the given data may be grouped. These categories could be in terms of similarities or characteristics or closeness of values. For instance, male or female groupings or age groups of 0-4 or 5-9, etc.
Class Intervals- are the distances between classes. For the age group 0-4 to 5-9, the distance is 5; between 0-5, and 4 to 9, it is also 5. The C>I. may then be obtained by