The first estimate for construction works given to a client is what he always remembers and is the estimate that often forms the basis upon which all other estimates are judged. At the stage when this estimate is being prepared, there is limited information about the project. This makes the preparation of an accurate first estimate for construction works difficult, more so because construction works are especially subject to risks and uncertainties at the inception stage. 

A factor that affects the quality of the first estimate is the contingency, which in most cases is included by estimators using no formal method of assessment. The assessment of an appropriate contingency sum requires an understanding of how estimators make budget contingency decisions and the impact of these decisions on the level of accuracy of the included contingency sum.  

Quantitative data on the factors that influenced the accuracy of contingency sums for building projects executed from 1995 to 2003 were collected from 83 registered quantity surveying firms in Nigeria. The respondents were asked to rate (using the Likert scale) the influence each of the 35 factors had on the accuracy of the contingency sum. Factor analysis and multivariate regression analysis were used to identify and quantify the factors and to establish a quantitative model that enables estimators to objectively estimate contingency allowance.