Comparison of Ward Population Estimates from FHSA Patient Registers with the 1991 Census

Postcode addresses from National Health Service patient registers for Norfolk and Suffolk current on census day 1991 were assigned to census wards, and estimates of populations in wards were produced for the total population and for twelve age—sex groups. These were compared with adjusted counts of usual residents from the 1991 Census. Regression analysis was used to identify the characteristics of wards with consistent differences between register estimates and census counts. Patient register estimates were less than census counts for children aged 0–4 years. Patient register estimates exceeded census counts for residents aged 15–44 years (especially males) and over 74 years. Wards with high rates of in-migration and high proportions of residents employed in the armed forces tended to have lower register estimates than census counts. Areas of high population density had higher register estimates than census counts. Taking these effects into account, about half the patient register estimates of total population were within 5% of the equivalent census figure, and 95% of wards had estimates within 20%. The main differences between patient register population estimates and census counts can be explained by delays in the updating of records in family health service authority (FHSA) registers and by undercounting in the 1991 Census. In Norfolk and Suffolk, FHSA registers are an acceptable alternative to the census for population estimation purposes. This supports recent arguments for wider use of population registers and suggests that they may be particularly valuable as a source of intercensal information.

Population dynamics of sewer rats

1. The effects of poison treatments on the rat populations of two sample districts of heavily infested sewers in a London borough were studied.2. Each district had a maximum rat population represented by a census figure of about 10,000 g. wheat eaten per day, corresponding to at least 400 rats.3. Poison treatments after prebaiting, at intervals of 6 months, reduced the rat population of each district to less than 10% of the maximum. A rapid restoration of the population followed, and the level reached in 6 months was near the maximum.4. In both areas, direct poisoning with sodium monofluoroacetate ‘1080’ was as effective as a prebaiting treatment. Direct poisoning with zinc phosphide was relatively unsuccessful.5. When both areas received double treatments, consisting of direct poisoning with sodium monofluoroacetate followed by a prebaiting treatment, the estimated population of one district was reduced to about 3% of the maximum. In the other area, rain made the second poisoning ineffective.6. The rate at which the population was restored from the 3% level was even higher than the rates previously observed, and was probably too high to be accounted for solely by breeding. Evidently, invasion from the surface played a part.7. No relationship could be established between the estimated sewer rat population densities within each district, and the known sites of surface infestation.We are grateful to the Council and officers of the Borough in which the work was done, for unstinted help throughout the inquiry. We also owe thanks to H. V. Thompson for help in the early stages; to him and to Miss M. D. A. Lawrence for discussing the work during its progress; to Miss M. M. Spencer for help in the analysis of the records and in checking calculations; and to A. G. Jenson for mapping the districts and for drawing the figures.