f u t u r e ra
Trendcurves
SUMMARY

LINEAR: Each time series is modeled using a straight line.

Equation:

Yt = at + b

, where Yt is the value of the time series at time t, and a and b are estimated from the data using least-squares estimation.

It seems that a horizontal line is a good fit for the slope characteristics. The slope of a straight line is constant, implying that Yt is increasing by a constant amount each period; if the slope is plotted against time a horizontal straight line is obtained and this is the required slope characteristic.

Many lines can be drawn. One that the application suggest is shown in the graph.

Equation where Y is the trend line.

Yt = 52.9t + 1048.5

Potential application: The linear curve type is useful for data that increases or decreases steadily with time. For example, this tool can be used to forecast the populations of communities during the stage of development in which the population growth is approximately linear.

BETA