# Analysing the Secular Trend

A number of different methods are available to estimate the trend; however, the suitability of these methods largely depends on the nature of the data and the purpose of the analysis. To measure a trend which can be represented as a straight line or some type of smooth curve, the following are the commonly employed methods:

**(1)** Freehand smooth curves

**(2)** Semi-average method

**(3)** Moving average method

**(4)** Mathematical curve fitting

Generally speaking, when the time series is available for a short span of time in which seasonal variation might be important, the freehand and semi-average methods are employed. If the available series is spread over a long time span and has annual data where long term cycles might be important, the moving average method and the mathematical curve fitting are generally employed.