4.10 Both the PPP contractor and the public sector client will need to collect comparative information. The PPP contractor will require this information for the purposes of identifying a benchmark cost of the services and the public sector client will need it to examine, interrogate and validate the results of the benchmark. However, this guidance allows, indeed encourages, use of common comparators and data to facilitate the negotiation and to reduce the input and costs for both parties. This is without prejudice to either party introducing additional sources at a later stage should the negotiation not succeed on the common set.