In the discrete time case, spells of receipt may be defined in terms of groups of consecutive intervals in receipt, but the accuracy of measurement of spells depends on how short the interval is. If observation of receipt is only annual or at one point within a year, short spells of receipt may be missed altogether. If a ‘benefit year’ is defined (for data-related reasons) as receipt at any time within a given year, as commonly done (see Annex 4.B), there is an asymmetric treatment of receipt relative to non-receipt. Only one week of receipt is needed to generate yi, = 1 for a benefit year, whereas non-receipt requires a full 52 weeks of non-receipt.