A linear regression modelling of the relation-ship 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.

Keywords: Relationship, initial & final construction time, project delivery

Abstrak
Die skatting van die konktrakvoltooiingstydperke was altyd inkorrek ten spyte daarvan dat daar ‘n behoefte is vir sekerheid betreffende die voltooiing van projekte. Hierdie artikel doen verslag oor ‘n ondersoek na die verhouding tussen aanvanklike en finale kontraktydperke met die doel om ‘n berekening vir redelike geskatte projekperiodes te ontwikkel. Data vir die studie is verkry uit ‘n totaal van agt en tagtig vraelyste en ses en vyftig projekte. Die steekproefpopulasie het bestaan uit argitekte, kontrakteurs, bourekenaars, strukturele ingenieurs en kliënte. Vyf metropoolstede, in die provinsies van die Oos-Kaap, Vrystaat, Gauteng, KwaZulu-Natal en Wes-Kaap, naamlik Bloemfontein, Kaapstad, Durban, Johannesburg en Port Elizabeth, het die geografiese gebied gevorm waarin die studie gedoen is. Inferensiële statistiese analise, insluitende regressive analise is gebruik om, onder andere, ‘n model en lineêre vergelykings om bou-konstruksie tydperke te skat, te ontwikkel. Die vergelykings wat ontwikkel is in die onderskeie fases van die studie is Y = 9.9 + 1.0586x vir fase een, en Y = 13.1159 + 1.1341x vir fase twee. Gedurende fase twee van die studie, is dit vasgestel dat 35.3% addisionele tyd tot die aanvanklike kontrakperiode bygevoeg behoort te word om die finale kontraktydperk te kan skat.
Daar word aanbeveel dat die vergelyking Y = 13.1159 + 1.1341x eerder gebruik word, of dat 35.3% addisionele tyd tot die getal van die aanvanklike kontraktydperk bygevoeg word om sodoende die finale kontraktydperk te
kan skat.

Sleutelwoorde: Verhouding, aanvanklike en finale kontraktydperke, projek lewering

Article text in English