Simple time trend (T) and quadratic time trend (T 2 ) Technological change is an improvement in the status of knowledge such that production possibilities are enhanced (Colman, 1983). It is an important cause of long term shifts in agricultural supply and includes changes in farming methods, adoption of physical capital and use of high yielding varieties and is usually captured using a time trend. Askari and Cummings (1977) made the justification that due to measurement problems and unavailability of data on specific variables, a simple time tend is used to capture effects of technological changes on output production overtime. Furthermore, Townsend and Thirtle (1997) justified the inclusion of a quadratic time trend stating that due to asset fixity in agriculture, adoption of technology cause
14 output to increase at a decreasing rate. Leaver (2004) also used the variables and found positive and negative signs for simple time trend and quadratic time trend. The same findings are also expected in this study.
