11.17 Most PPP contracts will stipulate that the unitary payment will increase by reference to RPI. To assist comparability participants should be instructed to use a uniform assumption for the inflation rate. Participants should also be able to demonstrate the effect on bids of using their preferred assumption for the rate of inflation, if this is different from the NHS body's instructed uniform inflation rate. It should be noted that different inflation assumptions will dramatically affect the funding cover ratios and returns to equity.