Trend by the Method of Semi-averages : This method can be used if a straight line trend is to be obtained. Since the location of only two points is necessary to obtain a straight line equation, it is obvious that we may select two representative points and connect them by a straight line. Data are divided into two halves and an average is obtained for each half. Each such average is shown against the mid-point of the half period, we obtain two points on a graph paper. By joining these points, a straight line trend is obtained.
The method is to be commended for its simplicity and used to some extent in practical work. This method is also flexible, for it is permissible to select representative periods to determine the two points. Unrepresentative years may be ignored.