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Parameters estimated by weighted least squares produced bad fits. The question is whether the fit can be improved by maximizing likelihood or using some alternative objective function. The concepts of likelihood, likelihood function, and maximum likelihood estimation will be explained and illustrated. In preparation for model development some commonly used likelihood functions will be given and implemented on a C-F spreadsheet. When the purpose of SPF development is to support practical road safety management, quality of fit rather than maximization of likelihood may be the preferred objective. The use of such alternative objective functions will prove both simple and attractive.