= Sampling frame
A <sampling frame> is the operational list or other device identifying the units from which a <statistical sample> can be selected. The intended <statistical population>, the <sampling frame> and the responding units can differ. A register of residential addresses, for example, can serve as a <sampling frame> for a household survey, but may miss newly built homes and include demolished buildings.
If 100 of 1000 target households are absent from the <sampling frame>, randomly selecting 90 of the 900 listed households gives each listed household <inclusion probability> $0.1$ and each omitted household <inclusion probability> zero. Increasing the sample among listed households cannot by itself correct that lack of coverage. Duplicate entries create a different problem: units with more entries can be more likely to be selected. A sound design therefore documents how frame units map to population units and distinguishes coverage errors from <sampling variability>.
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