A linear regression modelling of the relationship between initial estimated and final achieved construction time in South Africa

Abstract

The estimation of contract completion time has always been inaccurate despite there being a need for certainty regarding the completion of projects. This article reports on an investigation of the relationship between initial and final contract time with the aim of developing an equation for reasonably estimating project period. Data for the study was secured from a total of eighty-eight questionnaires and sixty-five projects. The sample population consisted of architects, contractors, quantity surveyors, structural engineers and clients. Five metropolitan cities in the provinces of the Eastern Cape, Free State, Gauteng, KwaZulu-Natal, and the Western Cape, namely Bloemfontein, Cape Town, Durban, Johannesburg and Port Elizabeth, constitute the geographical area in which the study was conducted. Inferential statistical analysis, including regression analysis, was used to evolve, inter alia, a model and linear equations for estimating building construction time. The equations involved in the respective phases of the study are Y = 9.9 + 1.0586x for phase one, and Y = 13.1159 + 1.1341x for phase two. During phase two of the study, it was determined that 35.3% additional time needs to be added to the amount of the initial contract period in order to estimate final contract time. It is recommended that either the equation Y = 13.1159 + 1.1341x be used, or that 35.3% additional time be added to the amount of initial contract time to estimate the final contract time.