The ONS LS was planned in the late 1960s at a time of considerable concern about the adequacy of mortality data collected from death registrations, and about the lack of data on fertility patterns. For example, when a death is registered, only very limited socio-economic information can be collected about the dead person, some of which (e.g. occupation) may be either deficient or inconsistent with that collected while the person was alive. More reliable and more extensive statistics could be obtained by linking the death record with the earlier census return for that person.
Similarly, the information provided on birth certificates did not allow for studies of birth spacing. Although such data could be obtained from the General Household Survey (GHS), the total sample sizes were too small for detailed studies.
The 1971 Census was the first to include a question on date of birth (rather than age), and this, combined with advances in information technology, made the ONS LS possible.