4.12 Overall both HM Treasury research and the earlier NAO sample suggest that PFI provides high levels of price certainty for the public sector, particularly in comparison to the budget overruns experienced in traditional procurement, demonstrating that construction risk had been effectively transferred to the private sector:
• in the HM Treasury sample, changes to the unitary charge were experienced in only one fifth of projects, and all were driven by changes in the requirements of the public sector client; and
• in the NAO sample, 21 per cent of projects surveyed involved a change in price for the public sector after contract award3 - and all were driven by a change in requirements by the public sector client.
PFI is therefore delivering very high levels of price certainty for the public sector for construction and operation, although of course at an early stage of the contract's life.

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