The 2015 target date for achieving the Millennium Development Goals (MDGs) is fast approaching, but there is very little discussion of the validity of the indicators used to measure progress. In particular, there has been little attention given to the problems that arise when assessments of progress are based on household surveys. These are inappropriate for obtaining information about the poorest of the poor. Typically, they omit by design those not in households because they are homeless; those who are in institutions; and mobile, nomadic or pastoralist populations; and, in practice, household surveys will typically under-represent those in fragile, disjointed or multiple occupancy households; and those in urban slums and insecure areas of a country. Those six subgroups constitute a pretty comprehensive ostensive definition of the "poorest of the poor." Between 300 and 500 million people--mainly in developing countries--will be missed worldwide from the sampling frames of household surveys.