D.2. Choice of reference period, periodicity of compilation and valuation of monetary variables
15.38. MSITS 2010 does not make any recommendation as to the choice of the reference period for compiling FATS. In practice, economies that compile FATS use years as a reference period. At the time of the present writing, such a choice seems reasonable from the perspective of users, as well as with respect to the reporting and compilation burden. However, in the future, there may be a need for data referring to shorter periods of time, e.g., quarters, at least for some main FATS aggregates.
15.39. MSITS 2010 does not make any recommendation as to the periodicity of update of FATS data, either. In practice, agencies producing FATS do so every year, at least for the variables that are deemed the most important (i.e., priority variables). In some cases it may be reasonable to consider compiling FATS less frequently (e.g. every odd year) for the variables and breakdowns of minor importance or for those that are most complicated to produce.
15.40. In principle, data for a given reference year should correspond to the calendar year, but firms may report on a fiscal or accounting year basis if that is what is available. In addition, it should be noted that some characteristics are compiled from already existing data, in particular for inward FATS. For those characteristics, the reference period may have to be taken as a given and might not always coincide with the calendar year. Compilers should clearly inform users of the reference period used, and whether there are any deviations for some variables.
15.41. Consistent with other economic statistics, activity should be recorded as it occurs rather than when the related payment is made (accrual basis). Flow variables should be recorded for the whole reference period, while stock variables should, if possible, be recorded from the end of the reference period. An exception is the employment variable, for which use of a period average is preferable (see also section D.4) if the employment is subject to strong seasonal variation. Data for a given reference period are mainly valued at the average prices and, if relevant, average exchange rates of that period. For stock variables (for example, property plant and equipment), values of source data might be recorded at historical cost and will largely reflect prices at the time the asset was acquired rather than the prices of the reference period. In such a case, revaluations to reflect current-period prices should be made by the compiler.
 Measuring Globalization: OECD Handbook on Economic Globalization Indicators (HEGI) recommends that the calendar year be used as a reference period.