Budgetary constraints are placing increasing pressure on project managers to effectively estimate development effort requirements at the earliest opportunity. With the rising impact of automation on commercial software development, the attention of researchers developing effort estimation models has recently been focused on functional representations of systems, in response to the assertion that development effort is a function of specification content. A number of such models exist; several, however, have received almost no research or industry attention. Project managers wishing to implement a functional assessment and estimation programme are therefore unlikely to be aware of the various methods or how they compare. This paper therefore provides this information, as well as forming a basis for the development and improvement of new methods