This paper investigates the nature of the relationship between software product size measured in Common Software Measurement International Consortium (COSMIC) Function Points and the development effort. We investigated both numerical and categorical cost factors which have a significant effect on this relationship based on the empirical studies we conducted using the International Software Benchmarking Standards Group (ISBSG) Dataset Release 10. For the statistical analyses, we performed step wise Analysis of Variance (ANOVA), Analysis of Co-Variance (ANCOVA) and Linear Regression Analysis techniques. In this paper, we discuss the results we obtained and the significance of the results for the software organizations who would like to improve their effort estimation processes.