Published price indexes are nearly always constructed from individual prices collected by somesampling framework, were the samples are chosen, in part, to minimize the time and expenseinvolved in collecting the prices. In particular, the time spent by reporting firms or consumers isquite rightly treated as precious. It is inevitable that questionnaires sent out in repeated monthswill sometimes not be returned. For example, about one-quarter of the individual items trackedunder the International Price Program (IPP) of the Bureau of Labor Statistics (BLS) do not report a price in any given month, though of these, about 60% eventually supply a price quote for thatmonth or a later month.