21 In examining the financial model for South Western our adviser found that although the model met bid requirements it was not a fully robust tool for medium or long term use on three grounds:
■ the large size of the business model and its complexity20;
■ the absence of built in supporting analysis for the revenue calculations - for example, the impact of crowding is a separate analysis - and for comprehensive evaluation of risk; and
■ the limited documentation provided to the Department explaining its use.
22 This means, in particular, that the model will not be easy to use for calculating the impact of a risk that the Department retains. It will also not be easy to use, as intended, to help reach agreement on re-setting the target revenues after substantial investments have been made by the Department or Network Rail.
___________________________________________________________________________________________
20 The overall model is so large that the opening of only two components: the Revenue Model and the Financial Model is enough to exceed the capacity of most computers. The developers supporting the Stagecoach bid must themselves have found this as shown by their solution to integrating the calculations: the cutting and pasting of large output data sheets from one model as input to the other. Such a vertical silo structure is difficult to maintain and after a period of no-usage, silo models can prove difficult to re-assimilate with confidence.