The predictive ability of Bromilow's time-cost model: a comment

The study of the relationship between construction time and cost has a long history. This paper reviews the report of Ng, S.T., Mak, M., Skitmore, R.M., Lam, K.C. and Varnam, M. (2001) Construction Management and Economics, 19, 165, and reveals they have made a substantial contribution to the method of analysis but that they have not sufficiently justified their case in light of the literature, and have not understood the role of sample sizes and confidence limits in the interpretation of their results. In particular, the present paper challenges their conclusion that a long term trend of improvement has been identified. This debate raises important epistemological questions for forecasting and modelling trends using generic time-cost models.