Productivity rates are among the most essential data needed in the construction industry. The accuracy of productivity rates is crucial for the determination of direct relationships between these rates and subjects such as estimating, cost control, scheduling, and resource management, among others. Past experience in the construction industry has shown that great variation in production rate values for the same construction item is attributed to the effects of project conditions which are commonly called influence factors. This paper describes the development of a statistical model that illustrates the quantitative relationships between influence factors and the productivity rates. The application of such a model will enable the user to estimate productivity rates with a higher degree of accuracy in future projects.