Farr's Law

Edward Higgs

In the nineteenth century the Western understanding of aetiology, the causes of death, changed fundamentally. The older Galenic understanding of disease and illness in terms of imbalances in the internal humours of unique human beings gave way to a new model in which diseases were seen as the effects of external pathogens on undifferentiated bodies. By the end of the century these pathogens were often understood in terms of germs, but in the earlier Victorian period they could be conceptualised in terms of miasma, or poisoning by chemicals in the environment. These chemicals could, in turn, be seen as the 'effluvia' of human bodies (Eyler, 96–122; Pelling).

William Farr, the Superintendent of Statistics in the General Register Office in London (GRO) from 1839 to 1879, was at the forefront of this changing understanding of disease in England (Higgs, 2004, 94–6). Farr, like many before him, was aware that mortality was higher in towns than in the countryside. However, because of the mortality data collected by the GRO via the civil registration system, Farr was able to show the difference statistically. In the 1850s, Farr developed the concept of the 'Healthy Districts' mortality experience based on a set of 63, mainly rural, registration districts whose crude death rate was below 17 per thousand. (See Healthy districts.) This was then compared to the higher mortality of urban areas to reveal 'excess' mortality, and thus gave local public health campaigners ammunition to push for local sanitary reform (Szreter, 439–40).

But Farr was also aware that mortality varied within urban areas, and worked towards understanding differences in mortality rates in terms of differences in population densities (Eyler, 132–3, 145–7). In the Fifth Annual Report of the Registrar General for England and Wales Farr ranked the metropolitan districts by population density and female mortality rate, and found that mortality seemed to increase as the sixth roots of the densities. This seemed to work quite well for the ten healthiest and the ten least healthy districts. Such a result fitted in with his general belief that the higher the density of population, the greater the number of deaths due to pathogens, in line with the new understanding of aetiology noted above. Farr saw these pathogens in terms of 'atmospheric impurities, organic matter undergoing decomposition, and the contagious principles of zymotic diseases' in the environment (Fifth Annual Report of the Registrar General for England and Wales, 203–15).

Farr returned to these ideas in the Fortieth Annual Report of the Registrar General, in which he tried to show that the higher the proximity of people in a place (and therefore the smaller the area for each person), the lower the mean duration of life. He still saw this as a reflection of the increased levels of pathogens in densely populated areas, referring to the presence of carbonic acid in the atmosphere, and of 'exhalations — smokes — of various kinds from dead matter, as well as from living bodies' (Fortieth Annual Report of the Registrar General, 231–8). However, Farr was groping towards understanding disease in terms of germ theory at this date (Eyler, 106–8).

Farr's 'law' of the impact of density on mortality had important implications, both for the GRO's data collection activities, and for the public health movement in general. It underlay the subsequent interest that the Office's medical statisticians showed in the effect of overcrowding on mortality rates into the 1930s and beyond (Higgs, 2004, 198–200). The desire to work out population densities was also one reason why the GRO not only wanted to know from the census the overall size of the population but also the number of people in particular administrative areas. This would also explain the interest shown in the censuses in the structure of households, in ages, in marital status, and in migration. These were seen as determinants of population growth, or as the mechanisms by which population was concentrated in the cities (Higgs, 1991). Slum clearance, the creation of the new towns, and the provision of parks, can all be seen in terms of a general belief that the lowering of population densities would reduce illness and mortality, and lead to well-being.

REFERENCES

John M. Eyler, Victorian social medicine. The ideas and methods of William Farr (London, 1979).

Fifth annual report of the Registrar General (1841) BPP 1843 XXI. (516) [View this document: Fifth annual report of the registrar-general]

Fortieth Annual Report of the Registrar General for England and Wales for 1877, BPP 1878–79 XIX [C.2276]. [View this document: Fortieth annual report of the registrar-general ]

Edward Higgs, 'Diseases, febrile poisons, and statistics: the census as a medical survey', Social History of Medicine, 4 (1991), 465–78.

Edward Higgs, 'The linguistic construction of social and medical categories in the work of the English General Register Office', in S. Szreter, A. Dharmalingam and H. Sholkamy, eds, The qualitative dimension of quantitative demography (Oxford, 2004), 86–106.

Margaret Pelling, Cholera, Fever and English Medicine, 1825–1865 (Oxford, 1978).

Simon Szreter, 'The GRO and the public health movement in Britain 1837–1914', Social History of Medicine, 4 (1991), 454–62.