  A quarter-century of statistical research has shown that census coverage
surveys, valuable as they are in offering a report card on each decennial
census, do not provide usable estimates of geographical differences in
coverage. The determining reason is the large number of ``doubly missing''
people missing both from the census enumeration and from coverage survey
estimates. Future coverage surveys should be designed to meet achievable goals,
foregoing efforts at spatial specificity. One implication is a sample size no
more than about $30,000$, setting free resources for controlling processing
errors and investing in coverage improvement. Possible integration of coverage
measurement with the American Community Survey would have many benefits and
should be given careful consideration.
