Guideline on how to convert ‘First Generation’ Function Point sizes to COSMIC sizes
‘First generation’ Functional Size Measurement (FSM) methods such as the IFPUG, MkII and Nesma methods and the ‘second generation’ COSMIC method all express their sizes in some variety of ‘Function Points’. However, the measurements are not directly comparable as each method has its own measurement rules and processes and hence different scales of measurement.
An organization wishing to move from using a first generation FSM method to using the COSMIC method will have two common questions:
Is there any formula to convert from one size scale to the COSMIC scale?
How accurate are the converted sizes likely to be (to help decide e.g. how to use the converted data to re-calibrate an estimating method)?
This Guideline aims to help answer this question, by describing:
the nature of the relationship between the size scales of first generation and COSMIC methods;
processes to establish a statistical relationship between first generation and COSMIC method sizes from a sample of software items that can be used for converting the first generation sizes of software items;
the results of studies to derive statistical conversion formulae from several sets of measurements of software sizes by first generation and by COSMIC methods;
other non-statistical methods of converting sizes measured by a first generation FSM method to COSMIC sizes.