(13)The historical time-span over which values for a given economic indicator are to be examined should be specified. A default time-span of 20 years should be set for each economic indicator. This is to ensure that the historical observation period covers at least two economic cycles. However, where those 20 years do not contain sufficiently severe values, institutions should be required to look further back into the data history. Values should be considered ‘not sufficiently severe’ if the variability of the economic indicator over that 20-year observation period is not representative of the likely range of variability of that indicator in the future.