Performance measurement systems and the publication of performance data are fundamental to the New Public Management, with its emphasis on decentralised service provision through a variety of agencies. There seem to be four reasons for this performance measurement: to see what works, to identify competences, to support public accountability and to allow control of decentralised service provision. Each of these is examined, using the root definitions that form part of soft systems methodology, which highlights the importance of different worldviews that provide justifications for different approaches to this measurement. If performance measurement systems are to be beneficial, their design should be based on a conceptualisations that recognises these different worldviews and purposes.