- Email: [email protected]
Differences in risk of mortality under 1 year of age between rural and urban areas: an ecological study
Public Health (2005) 119, 442–447
Differences in risk of mortality under 1 year of age between rural and urban areas: an ecological study Z.E.S. Guildeaa,*, D.L. Fonea, F.D. Dunstana, P.H.T. Cartlidgeb a
Department of Epidemiology, Statistics and Public Health, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK b Department of Child Health, Cardiff University, Cardiff, UK Received 27 January 2004; received in revised form 23 July 2004; accepted 7 August 2004 Available online 21 December 2004
KEYWORDS Rural health; Infant mortality; Social deprivation; Ecological study
Summary Objective. To investigate differences in risk of categories and causes of death before 1 year of age between rural and urban areas. Methods. Population-based ecological study using Poisson regression analysis of data from all enumeration districts in Wales. Data included all 243 223 registrable births to women resident in Wales, 809 therapeutic and spontaneous abortions, 1302 stillbirths and 1418 infant deaths occurring between 1993 and 1999. Main results. The relative risk of mortality in rural areas compared with urban areas for all deaths before 1 year of age was 0.89 (95% confidence interval 0.82, 0.98, PZ0.02). The risk of mortality in rural areas was significantly lower than in urban areas for all categories of deaths occurring after 7 days of life. The relative risk of death due to infection was significantly lower in rural areas compared with urban areas (PZ0.04), with similar results for deaths due to sudden infant death syndrome (PZ0.03). After adjusting for social deprivation, there were no significant differences in the risk of death between rural and urban areas. Conclusions. While there were significant differences in crude risk between rural and urban enumeration districts for some causes and age groups before 1 year, after adjusting for social deprivation, these differences were not significant. The lack of significant interaction between rurality and deprivation indicated that the relationship between social deprivation and death before 1 year of age was not significantly different in rural areas compared with urban areas. Collaborative public health programmes to tackle deprivation are necessary in both rural and urban areas. Q 2004 The Royal Institute of Public Health. Published by Elsevier Ltd. All rights reserved.
Introduction
* Corresponding author. Tel.: C44 2920 748293; fax: C44 2920 742898. E-mail address: [email protected] (Z.E.S. Guildea).
The issue of rural public health, in comparison to urban health, has been largely neglected in the UK.1,2 Research on rural health has tended to focus on the investigation of how poor access to health
0033-3506/$ - see front matter Q 2004 The Royal Institute of Public Health. Published by Elsevier Ltd. All rights reserved.
Risk of mortality under 1 year of age in rural and urban areas services is associated with lower uptake of treatment and poorer outcome.2 However, a review of evidence on the problems facing rural health and health care in the UK found that, despite the problem of access to services, levels of rural health do not seem to be worse than those in urban areas.3 Although there are wide regional variations in perinatal and infant mortality rates in Britain,4 there is little published evidence on whether maternal residence in a rural or urban area is associated with early childhood mortality. Chamberlain reported that the perinatal mortality rate in the early 1970 s was lower in rural areas compared with urban areas within every region of the UK.5 More recently, a study of a large sample of births registered in Cumbria suggested that the risk of stillbirth was significantly lower outside major urban centres. However, the risk was not significantly lower in rural areas defined using Land Use Surveys.6 In a previous small-area ecological study of stillbirths and infant deaths in Wales, a country with a substantial rural population, we showed that death rates for all age groups, except early neonatal (see Appendix for definition of age groups), were associated with enumeration district level area deprivation.7 In view of the lack of evidence relating early childhood mortality to the urban or rural nature of residence, the aim of this study was to investigate rural/urban differences in the risk of death before 1 year of age and their relationship with area-based social deprivation.
Methods The data in this study relate to births between 1993 and 1999 to women resident in Wales, irrespective of the place of delivery. Live births were identified from the Child Health System (CHS) database,8 which collects data from the birth notification form. Data on therapeutic and spontaneous abortions, stillbirths and infant deaths were identified from the All Wales Perinatal Survey (AWPS), a population-based register of mortality between 20 completed weeks of gestation and 1 year of age.9 During these 7 complete years, there were 243 223 registrable births, 809 therapeutic and spontaneous abortions, 1302 stillbirths and 1418 infant deaths. Information about each death was collected on the survey questionnaire, which included detailed clinical information about the mother and the baby (sex, birth weight, gestational age, clinical management and postmortem findings). This information was
443
used to classify the cause of death according to the clinicopathological system, modified to clarify certain ambiguities and expanded to take account of postneonatal deaths.10,11 Complete ascertainment of mortality was verified by the AWPS regional co-ordinating team by cross-checking with data from the CHS database and the Office for National Statistics (ONS). The ecological area of analysis in this study is the 1991 census enumeration district. There are 6401 residential enumeration districts in Wales, each containing approximately 200 households and a mean population of 443. We defined rurality using the ONS urban/rural classification of enumeration districts, obtained from the census dissemination unit.12 The 26% of enumeration districts defined as rural contain 19% of the population and represent 85% of the total land mass of 8016 square miles. All births and deaths were assigned using postcode linkage to the enumeration district of residence using Postpoint Professional in Map Info, version 5.5. The accuracy of the postcode was checked using the Post Office PAF computer file that links address to postcode. Postcodes were missing or invalid in 3232 (1.3%) registrable births and three (0.1%) deaths; these cases were excluded from the analysis. We used the enumeration district Townsend score as the measure of social deprivation.13 This is calculated using unemployment, car ownership, owner occupation and overcrowding variables derived from 1991 census data. The individual score for each component was standardized to zero mean and unit variance across the enumeration districts in England and Wales. The Townsend score ranged from K7.55 to C10.79 in the leastdeprived and most-deprived enumeration districts, respectively.
Analysis We calculated crude rates for each age group and cause of death for aggregate urban and rural areas, and compared the relative risk of death in urban and rural areas using 95% confidence intervals (CI). We quantified the associations between the various age groups and causes of death and urban/rural status, adjusting for the Townsend score using Poisson regression on data from individual enumeration districts. To determine whether the effect of deprivation on mortality rates was different in rural areas compared with urban areas, we included an interaction term between the Townsend score and rurality in each model.
444
Z.E.S. Guildea et al. The mean Townsend score in rural enumeration districts was lower than in urban enumeration districts (K1.53, SD 2.24 compared with 0.53, SD 3.4), suggesting that rural areas are less deprived than urban areas. After adjustment for the Townsend score, the rural or urban nature of the enumeration district was no longer significantly associated with death (Table 2). The Townsend score was highly significant, and examination of the deviance showed that it was responsible for the majority of the variation explained by the model. However, these results do not necessarily rule out an association with rurality. For late neonatal deaths, for example, the 95%CI of 0.43–1.05 is compatible with a halving of risk in rural enumeration districts. When the interaction term between rurality and the Townsend score was added to the models, there was no significant reduction in deviance. There was, therefore, no evidence that the relationship between deprivation and mortality was different in rural areas compared with urban areas.
From the parameter estimates of each model, we calculated the magnitude of the effect, defined as the percentage change in the mortality rate arising from a unit change in the Townsend score. From this, we estimated the percentage increase in the mortality rate between the 25th and 75th centiles of the enumeration district distribution of Townsend scores. Analyses were performed using SAS version 8 and SPSS version 11.5.
Results The crude mortality rates for all deaths between 20 weeks of gestation and 1 year of age were 13.4 per 1000 registrable births in rural areas and 15.0 per 1000 in urban areas (difference in rates 1.6/1000; 95%CI 0.03–0.28, PZ0.02). This is equivalent to a relative risk of death of 0.89 (95%CI 0.82–0.98). Table 1 shows the relative risk of death in rural areas compared with urban areas for each age group and cause of death. The risk of death was significantly lower in rural areas in the late neonatal, postneonatal and infant categories, and infection and sudden infant death syndrome causes of death. There were no significant differences between rural and urban risk for the other categories and causes of death. Table 1
Discussion The results of this population-based ecological study show that the crude risk of death in infants aged between 7 days and 1 year and the risk of
Relative risk of death in rural enumeration districts compared with urban enumeration districts. Rate/1000 (number of deaths)
Categories of death Therapeutic abortions Spontaneous abortions Stillbirths Early neonatal Perinatal Late neonatal Neonatal Postneonatal Infant Total deaths Causes of death Congenital anomaly Unexplained stillbirth Placental abruption Intrapartum event Prematurity Infection Specific conditions and accidental death Sudden infant death syndrome
RR (95% CI)
P value
Rural
Urban
1.48 1.84 4.94 3.14 8.06 0.59 3.71 1.41 5.12 13.4
(58) (72) (193) (122) (315) (23) (145) (55) (200) (523)
1.29 2.08 5.53 2.88 8.39 0.99 3.84 2.23 6.06 15.0
(259) (418) (1109) (574) (1683) (197) (771) (446) (1217) (3003)
1.15 0.88 0.89 1.09 0.96 0.60 0.97 0.63 0.84 0.89
(0.87, (0.69, (0.77, (0.90, (0.85, (0.39, (0.81, (0.48, (0.73, (0.82,
1.53) 1.14) 1.04) 1.33) 1.08) 0.92) 1.15) 0.84) 0.98) 0.98)
0.34 0.34 0.15 0.38 0.52 0.02 0.7 0.001 0.03 0.02
3.12 (122) 3.91 (153) 1.15 (45) 0.87 (34) 2.02 (79) 0.82 (32) 0.9 (35)
3.20 4.46 1.12 0.81 2.39 1.21 0.88
(643) (895) (224) (163) (480) (242) (177)
0.97 0.88 1.03 1.07 0.85 0.68 1.02
(0.80, (0.74, (0.75, (0.74, (0.67, (0.47, (0.71,
1.18) 1.04) 1.42) 1.55) 1.07) 0.98) 1.46)
0.79 0.14 0.85 0.72 0.17 0.04 0.93
0.51 (20)
0.86 (173)
0.59 (0.37, 0.94)
0.03
Risk of mortality under 1 year of age in rural and urban areas
445
Table 2 Poisson regression model of effect of rurality after adjustment for Townsend score, for each category and cause of death. Rural vs. urban
Categories of death Therapeutic abortions Spontaneous abortions Stillbirths Early neonatal Perinatal Late neonatal Neonatal Postneonatal Infant deaths Total deaths Causes of death Congenital anomaly Unexplained stillbirth Placental abruption Intrapartum event Prematurity Infection Specific conditions and accidental death Sudden infant death syndrome
Townsend a
P value
OR (95% CI)
P value
% Increase over IQRb (95% CI)
0.37 0.92 0.66 0.18 0.66 0.07 0.76 0.12 0.53 0.73
1.14 1.01 0.97 1.15 1.03 0.67 1.03 0.79 0.95 0.98
(0.85, (0.78, (0.82, (0.93, (0.91, (0.43, (0.85, (0.59, (0.81, (0.89,
1.54) 1.32) 1.13) 1.41) 1.17) 1.05) 1.24) 1.06) 1.11) 1.08)
0.87 !0.0001 !0.0001 0.04 !0.0001 0.01 !0.01 !0.0001 !0.0001 !0.0001
K1.2 (K14.6, 14.4) 29.4 (15.7, 44.6) 16.3 (8.5, 24.7) 10.4 (2.7, 21.6) 14.2 (8.0, 20.9) 23.2 (4.3, 45.5) 13.5 (4.4, 23.4) 50.8 (35.4, 68.0) 26.0 (18.0, 34.5) 20.2 (15.2, 25.4)
0.87 0.62 0.64 0.55 0.32 0.17 0.34
1.02 0.96 1.16 1.12 0.88 0.77 1.20
(0.83, (0.80, (0.83, (0.76, (0.69, (0.52, (0.82,
1.25) 1.14) 1.63) 1.66) 1.13) 1.12) 1.76)
0.06 !0.0001 !0.01 0.30 0.10 !0.01 !0.001
9.0 (K0.6, 19.5) 18.2 (9.4, 27.7) 26.0 (8.2, 46.7) 9.8 (K8.5, 31.6) 9.2 (K1.9, 21.6) 25.8 (8.3, 46.1) 36.6 (15.2, 61.9)
0.66
0.90 (0.55, 1.46)
!0.0001
101.0 (69.2, 138.7)
a
Odds ratio of mortality for rural vs urban areas after adjustment for Townsend score of deprivation. Percentage increase in mortality rate between 25th and 75th centile of distribution of Townsend scores in enumeration districts in Wales. b
death from infection and sudden infant death syndrome were significantly lower in rural areas compared with urban areas. There was no significant excess risk in rural areas for any category or cause of death. After adjustment for the enumeration district deprivation score, there was no significant difference in the risk of death between rural and urban areas, suggesting that deprivation is more strongly associated with death in infancy than urban residence.
Comparison with other literature A study of 280 757 singleton births in Cumbria, UK between 1950 and 1992 reported a reduction in the risk of stillbirth to mothers living outside a major built-up area (defined using Bartholomew boundaries of built-up areas in a geographical information system) between 1966 and 1992 (odds ratio 0.82, 95% CI 0.73–0.92), after adjusting for father’s social class.6 However, no excess urban risk was found when rurality was defined according to the 1961 and 1989 Land Use Surveys, which are similar to the ONS classification, and so our
findings of no reduced risk for stillbirth in rural areas are consistent with their study. Clearly the results may be sensitive to the classification of rurality used. We also found no interaction between urban/rural status and area deprivation, providing more evidence that the effects of deprivation on the risk of stillbirth did not differ significantly between urban and rural births. To our knowledge, no other published analyses have estimated the risk for all of the standard categories of death from 24 weeks of gestation to 1 year of life and for a wide variety of causes of death.
Strengths and weaknesses of the study This was a large-scale study using data on births and deaths over a 7-year period from the 6376 enumeration districts in Wales which recorded births. We used data on deaths from the AWPS, a robust data set where complete ascertainment of deaths between 24 weeks of gestation and 1 year of life is accurately verified using records from the ONS and the Welsh Child Health System.
446 In this study, we used the ONS enumeration district classification.12 This is based upon a definition of land that is ‘irreversibly urban in character’ in the National Land Use Classification and is independent of administrative boundaries.14 An enumeration district was then defined as urban if the majority of its population resided in defined urban land within the enumeration district. All other enumeration districts were classified as rural. The classification of geographical areas into urban and rural has no agreed or standard definition. The literature describes a variety of approaches, including settlement size, population density, nearest neighbour, accessibility and multivariate area classification.15 Given the lack of consensus on a definition of rurality, it has been suggested that practical and sensible definitions appropriate for the particular study in question should be employed.2 Although the ONS classification based on land use is open to criticism for failing to acknowledge the wider social and economic differences that exist in rural areas,16 it was the most suitable for our study since we were able to model urban/rural status using a national definition at the smallest geographical level available, the enumeration district, to address the aims of this study. Since data on maternal socio-economic status are not systematically available for births in Wales, we used the Townsend score as the ecological adjustment for deprivation. There is an unresolved debate over the appropriateness of the use of deprivation indices in rural areas,2 since urbanbased deprivation indices may fail to identify pockets of deprivation in rural areas due to the dispersed and heterogeneous nature of rural populations.17 These indices include census variables that may be better proxies for low incomes in urban compared with rural populations. For example, the inclusion of the car ownership variable has been shown to be less valid for use in sparsely populated rural areas.18 In this study, exclusion of the car ownership variable from the Townsend score calculation recategorized rural enumeration districts as more deprived compared with the standard score. In our study, we have shown that the effect of the Townsend score on mortality rates before 1 year of age is not significantly different between rural and urban areas, so that the Townsend score can be used as a measure of deprivation for both rural and urban areas. Using the Townsend score rather than social class to adjust for deprivation raises the possibility of ecological bias.19 We would have preferred to model the data in a multilevel analysis20 to adjust for social deprivation at the individual level and estimate more precise parameter coefficients for urban/rural status at
Z.E.S. Guildea et al. the higher enumeration district level, but this was not possible without data on individual socioeconomic status. These results confirm our previous findings that social deprivation is significantly associated with several categories and causes of death under 1 year of age.7 Although the crude risk of death is lower in rural enumeration districts in Wales, we found no differences in this study between rural and urban enumeration districts after adjusting for deprivation. As we have argued previously,7 collaborative public health programmes to reduce individual and area-wide inequalities in the determinants of health are important. The results of this study suggest that it is necessary to tackle deprivation in rural areas as well as urban areas.
Acknowledgements We would like to thank the staff of All Wales Perinatal Survey for their assistance with the study.
Appendix Category of death
Definition
Therapeutic abortion
Therapeutic late fetal deaths before 24 weeks of gestation Spontaneous late fetal deaths before 24 weeks of gestation Late fetal deaths after 24 weeks of gestation Deaths occurring in the first 6 days of life Stillbirths and deaths in the first 6 days of life Deaths at 7–27 completed days of life Deaths in the first 27 completed days of life Deaths between 28 days and 1 year Deaths under 1 year of age (excluding stillbirths)
Spontaneous abortion Stillbirths Early neonatal Perinatal Late neonatal Neonatal Postneonatal Infant
References 1. Phillimore P, Reading R. A rural advantage? Urban–rural health differences in Northern England J Public Health Med 1992;14:290–9. 2. Farmer JC, Baird AG, Iversen L. Rural deprivation: reflecting reality. Br J Gen Pract 2001;51:486–91.
Risk of mortality under 1 year of age in rural and urban areas 3. Watt IS, Franks AJ, Sheldon TA. Health and health care of rural populations in the UK: is it better or worse? J Epidemiol Community Health 1994;48:16–21. 4. MacFarlane A, Mugford M. Variations in births and deaths. In: MacFarlane A, Mugford M, editors. Birth Counts: statistics of pregnancy and childbirth. London: HMSO; 2000. 5. Chamberlain G. Background to perinatal health. Lancet 1979;2:1061–3. 6. Dickinson HO, Hutton JL, Greaves LH, Dummer TJ, Parker L. Deprivation and stillbirth risk in rural and urban areas. Paediatr Perinat Epidemiol 2002;16:249–54. 7. Guildea ZES, Fone DL, Dunstan FD, Sibert JR, Cartlidge PH. Social deprivation and the causes of stillbirth and infant mortality. Arch Dis Child 2001;84:307–10. 8. Andrews J, Cotter M, Richards R, Lewis D. Report on maternal data/information aspects of the child health system. Cardiff: Welsh Office; 1996. 9. Cartlidge PHT, Stewart JH, Hopkins JM, Guildea ZES, Rolpe K, Mundy KE. All Wales Perinatal Survey and Confidential Enquiry into Stillbirths and Deaths in Infancy Annual Report 1998. Cardiff: Perinatal Survey Office; 1998. 10. Wigglesworth JS. Monitoring perinatal mortality. A pathophysiological approach. Lancet 1980;2:684–6. 11. Keeling JW, MacGillivray I, Golding J, Wigglesworth J, Berry J, Dunn PM. Classification of perinatal death. Arch Dis Child 1989;64:1345–51.
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12. Office for National Statistics. 1991 Census: urban/rural ward categorisation. London: Office for National Statistics Factsheet; 1992. 13. Townsend P, Phillimore P, Beattie A. Health and deprivation: inequality in the north. London: Routledge; 1988. 14. Joint Local Authority, LAMSAC, SDD and Department of the Environment Study Team. The national land use classification. London: HMSO; 1975. 15. Martin D, Brigham P, Roderick P, Bournett S, Diamond I. The (mis)representation of rural deprivation. Environ Plan A 2000;32:735–51. 16. Denham C. Urban Britain: a new study of urban land and population. In: Population trends 36. London: HMSO; 1984. 17. Payne G, Payne J, Hyde M. Refuse of all classes? Social indicators and social deprivation Sociological Research Online 1996;1:1–25. 18. Christie SML, Fone DL. Does car ownership reflect socioeconomic disadvantage in rural areas? A cross-sectional geographical study in Wales, UK Public Health 2003;117: 112–6. 19. Greenland S. Ecologic versus individual-level sources of bias in ecologic estimates of contextual health effects. Int J Epidemiol 2001;30:1343–50. 20. Duncan C, Jones K, Moon G. Context, composition and heterogeneity: using multilevel models in health research. Soc Sci Med 1998;46:97–117.
Differences in risk of mortality under 1 year of age between rural and urban areas: an ecological study Z.E.S. Guildeaa,*, D.L. Fonea, F.D. Dunstana, P.H.T. Cartlidgeb a
Department of Epidemiology, Statistics and Public Health, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK b Department of Child Health, Cardiff University, Cardiff, UK Received 27 January 2004; received in revised form 23 July 2004; accepted 7 August 2004 Available online 21 December 2004
KEYWORDS Rural health; Infant mortality; Social deprivation; Ecological study
Summary Objective. To investigate differences in risk of categories and causes of death before 1 year of age between rural and urban areas. Methods. Population-based ecological study using Poisson regression analysis of data from all enumeration districts in Wales. Data included all 243 223 registrable births to women resident in Wales, 809 therapeutic and spontaneous abortions, 1302 stillbirths and 1418 infant deaths occurring between 1993 and 1999. Main results. The relative risk of mortality in rural areas compared with urban areas for all deaths before 1 year of age was 0.89 (95% confidence interval 0.82, 0.98, PZ0.02). The risk of mortality in rural areas was significantly lower than in urban areas for all categories of deaths occurring after 7 days of life. The relative risk of death due to infection was significantly lower in rural areas compared with urban areas (PZ0.04), with similar results for deaths due to sudden infant death syndrome (PZ0.03). After adjusting for social deprivation, there were no significant differences in the risk of death between rural and urban areas. Conclusions. While there were significant differences in crude risk between rural and urban enumeration districts for some causes and age groups before 1 year, after adjusting for social deprivation, these differences were not significant. The lack of significant interaction between rurality and deprivation indicated that the relationship between social deprivation and death before 1 year of age was not significantly different in rural areas compared with urban areas. Collaborative public health programmes to tackle deprivation are necessary in both rural and urban areas. Q 2004 The Royal Institute of Public Health. Published by Elsevier Ltd. All rights reserved.
Introduction
* Corresponding author. Tel.: C44 2920 748293; fax: C44 2920 742898. E-mail address: [email protected] (Z.E.S. Guildea).
The issue of rural public health, in comparison to urban health, has been largely neglected in the UK.1,2 Research on rural health has tended to focus on the investigation of how poor access to health
0033-3506/$ - see front matter Q 2004 The Royal Institute of Public Health. Published by Elsevier Ltd. All rights reserved.
Risk of mortality under 1 year of age in rural and urban areas services is associated with lower uptake of treatment and poorer outcome.2 However, a review of evidence on the problems facing rural health and health care in the UK found that, despite the problem of access to services, levels of rural health do not seem to be worse than those in urban areas.3 Although there are wide regional variations in perinatal and infant mortality rates in Britain,4 there is little published evidence on whether maternal residence in a rural or urban area is associated with early childhood mortality. Chamberlain reported that the perinatal mortality rate in the early 1970 s was lower in rural areas compared with urban areas within every region of the UK.5 More recently, a study of a large sample of births registered in Cumbria suggested that the risk of stillbirth was significantly lower outside major urban centres. However, the risk was not significantly lower in rural areas defined using Land Use Surveys.6 In a previous small-area ecological study of stillbirths and infant deaths in Wales, a country with a substantial rural population, we showed that death rates for all age groups, except early neonatal (see Appendix for definition of age groups), were associated with enumeration district level area deprivation.7 In view of the lack of evidence relating early childhood mortality to the urban or rural nature of residence, the aim of this study was to investigate rural/urban differences in the risk of death before 1 year of age and their relationship with area-based social deprivation.
Methods The data in this study relate to births between 1993 and 1999 to women resident in Wales, irrespective of the place of delivery. Live births were identified from the Child Health System (CHS) database,8 which collects data from the birth notification form. Data on therapeutic and spontaneous abortions, stillbirths and infant deaths were identified from the All Wales Perinatal Survey (AWPS), a population-based register of mortality between 20 completed weeks of gestation and 1 year of age.9 During these 7 complete years, there were 243 223 registrable births, 809 therapeutic and spontaneous abortions, 1302 stillbirths and 1418 infant deaths. Information about each death was collected on the survey questionnaire, which included detailed clinical information about the mother and the baby (sex, birth weight, gestational age, clinical management and postmortem findings). This information was
443
used to classify the cause of death according to the clinicopathological system, modified to clarify certain ambiguities and expanded to take account of postneonatal deaths.10,11 Complete ascertainment of mortality was verified by the AWPS regional co-ordinating team by cross-checking with data from the CHS database and the Office for National Statistics (ONS). The ecological area of analysis in this study is the 1991 census enumeration district. There are 6401 residential enumeration districts in Wales, each containing approximately 200 households and a mean population of 443. We defined rurality using the ONS urban/rural classification of enumeration districts, obtained from the census dissemination unit.12 The 26% of enumeration districts defined as rural contain 19% of the population and represent 85% of the total land mass of 8016 square miles. All births and deaths were assigned using postcode linkage to the enumeration district of residence using Postpoint Professional in Map Info, version 5.5. The accuracy of the postcode was checked using the Post Office PAF computer file that links address to postcode. Postcodes were missing or invalid in 3232 (1.3%) registrable births and three (0.1%) deaths; these cases were excluded from the analysis. We used the enumeration district Townsend score as the measure of social deprivation.13 This is calculated using unemployment, car ownership, owner occupation and overcrowding variables derived from 1991 census data. The individual score for each component was standardized to zero mean and unit variance across the enumeration districts in England and Wales. The Townsend score ranged from K7.55 to C10.79 in the leastdeprived and most-deprived enumeration districts, respectively.
Analysis We calculated crude rates for each age group and cause of death for aggregate urban and rural areas, and compared the relative risk of death in urban and rural areas using 95% confidence intervals (CI). We quantified the associations between the various age groups and causes of death and urban/rural status, adjusting for the Townsend score using Poisson regression on data from individual enumeration districts. To determine whether the effect of deprivation on mortality rates was different in rural areas compared with urban areas, we included an interaction term between the Townsend score and rurality in each model.
444
Z.E.S. Guildea et al. The mean Townsend score in rural enumeration districts was lower than in urban enumeration districts (K1.53, SD 2.24 compared with 0.53, SD 3.4), suggesting that rural areas are less deprived than urban areas. After adjustment for the Townsend score, the rural or urban nature of the enumeration district was no longer significantly associated with death (Table 2). The Townsend score was highly significant, and examination of the deviance showed that it was responsible for the majority of the variation explained by the model. However, these results do not necessarily rule out an association with rurality. For late neonatal deaths, for example, the 95%CI of 0.43–1.05 is compatible with a halving of risk in rural enumeration districts. When the interaction term between rurality and the Townsend score was added to the models, there was no significant reduction in deviance. There was, therefore, no evidence that the relationship between deprivation and mortality was different in rural areas compared with urban areas.
From the parameter estimates of each model, we calculated the magnitude of the effect, defined as the percentage change in the mortality rate arising from a unit change in the Townsend score. From this, we estimated the percentage increase in the mortality rate between the 25th and 75th centiles of the enumeration district distribution of Townsend scores. Analyses were performed using SAS version 8 and SPSS version 11.5.
Results The crude mortality rates for all deaths between 20 weeks of gestation and 1 year of age were 13.4 per 1000 registrable births in rural areas and 15.0 per 1000 in urban areas (difference in rates 1.6/1000; 95%CI 0.03–0.28, PZ0.02). This is equivalent to a relative risk of death of 0.89 (95%CI 0.82–0.98). Table 1 shows the relative risk of death in rural areas compared with urban areas for each age group and cause of death. The risk of death was significantly lower in rural areas in the late neonatal, postneonatal and infant categories, and infection and sudden infant death syndrome causes of death. There were no significant differences between rural and urban risk for the other categories and causes of death. Table 1
Discussion The results of this population-based ecological study show that the crude risk of death in infants aged between 7 days and 1 year and the risk of
Relative risk of death in rural enumeration districts compared with urban enumeration districts. Rate/1000 (number of deaths)
Categories of death Therapeutic abortions Spontaneous abortions Stillbirths Early neonatal Perinatal Late neonatal Neonatal Postneonatal Infant Total deaths Causes of death Congenital anomaly Unexplained stillbirth Placental abruption Intrapartum event Prematurity Infection Specific conditions and accidental death Sudden infant death syndrome
RR (95% CI)
P value
Rural
Urban
1.48 1.84 4.94 3.14 8.06 0.59 3.71 1.41 5.12 13.4
(58) (72) (193) (122) (315) (23) (145) (55) (200) (523)
1.29 2.08 5.53 2.88 8.39 0.99 3.84 2.23 6.06 15.0
(259) (418) (1109) (574) (1683) (197) (771) (446) (1217) (3003)
1.15 0.88 0.89 1.09 0.96 0.60 0.97 0.63 0.84 0.89
(0.87, (0.69, (0.77, (0.90, (0.85, (0.39, (0.81, (0.48, (0.73, (0.82,
1.53) 1.14) 1.04) 1.33) 1.08) 0.92) 1.15) 0.84) 0.98) 0.98)
0.34 0.34 0.15 0.38 0.52 0.02 0.7 0.001 0.03 0.02
3.12 (122) 3.91 (153) 1.15 (45) 0.87 (34) 2.02 (79) 0.82 (32) 0.9 (35)
3.20 4.46 1.12 0.81 2.39 1.21 0.88
(643) (895) (224) (163) (480) (242) (177)
0.97 0.88 1.03 1.07 0.85 0.68 1.02
(0.80, (0.74, (0.75, (0.74, (0.67, (0.47, (0.71,
1.18) 1.04) 1.42) 1.55) 1.07) 0.98) 1.46)
0.79 0.14 0.85 0.72 0.17 0.04 0.93
0.51 (20)
0.86 (173)
0.59 (0.37, 0.94)
0.03
Risk of mortality under 1 year of age in rural and urban areas
445
Table 2 Poisson regression model of effect of rurality after adjustment for Townsend score, for each category and cause of death. Rural vs. urban
Categories of death Therapeutic abortions Spontaneous abortions Stillbirths Early neonatal Perinatal Late neonatal Neonatal Postneonatal Infant deaths Total deaths Causes of death Congenital anomaly Unexplained stillbirth Placental abruption Intrapartum event Prematurity Infection Specific conditions and accidental death Sudden infant death syndrome
Townsend a
P value
OR (95% CI)
P value
% Increase over IQRb (95% CI)
0.37 0.92 0.66 0.18 0.66 0.07 0.76 0.12 0.53 0.73
1.14 1.01 0.97 1.15 1.03 0.67 1.03 0.79 0.95 0.98
(0.85, (0.78, (0.82, (0.93, (0.91, (0.43, (0.85, (0.59, (0.81, (0.89,
1.54) 1.32) 1.13) 1.41) 1.17) 1.05) 1.24) 1.06) 1.11) 1.08)
0.87 !0.0001 !0.0001 0.04 !0.0001 0.01 !0.01 !0.0001 !0.0001 !0.0001
K1.2 (K14.6, 14.4) 29.4 (15.7, 44.6) 16.3 (8.5, 24.7) 10.4 (2.7, 21.6) 14.2 (8.0, 20.9) 23.2 (4.3, 45.5) 13.5 (4.4, 23.4) 50.8 (35.4, 68.0) 26.0 (18.0, 34.5) 20.2 (15.2, 25.4)
0.87 0.62 0.64 0.55 0.32 0.17 0.34
1.02 0.96 1.16 1.12 0.88 0.77 1.20
(0.83, (0.80, (0.83, (0.76, (0.69, (0.52, (0.82,
1.25) 1.14) 1.63) 1.66) 1.13) 1.12) 1.76)
0.06 !0.0001 !0.01 0.30 0.10 !0.01 !0.001
9.0 (K0.6, 19.5) 18.2 (9.4, 27.7) 26.0 (8.2, 46.7) 9.8 (K8.5, 31.6) 9.2 (K1.9, 21.6) 25.8 (8.3, 46.1) 36.6 (15.2, 61.9)
0.66
0.90 (0.55, 1.46)
!0.0001
101.0 (69.2, 138.7)
a
Odds ratio of mortality for rural vs urban areas after adjustment for Townsend score of deprivation. Percentage increase in mortality rate between 25th and 75th centile of distribution of Townsend scores in enumeration districts in Wales. b
death from infection and sudden infant death syndrome were significantly lower in rural areas compared with urban areas. There was no significant excess risk in rural areas for any category or cause of death. After adjustment for the enumeration district deprivation score, there was no significant difference in the risk of death between rural and urban areas, suggesting that deprivation is more strongly associated with death in infancy than urban residence.
Comparison with other literature A study of 280 757 singleton births in Cumbria, UK between 1950 and 1992 reported a reduction in the risk of stillbirth to mothers living outside a major built-up area (defined using Bartholomew boundaries of built-up areas in a geographical information system) between 1966 and 1992 (odds ratio 0.82, 95% CI 0.73–0.92), after adjusting for father’s social class.6 However, no excess urban risk was found when rurality was defined according to the 1961 and 1989 Land Use Surveys, which are similar to the ONS classification, and so our
findings of no reduced risk for stillbirth in rural areas are consistent with their study. Clearly the results may be sensitive to the classification of rurality used. We also found no interaction between urban/rural status and area deprivation, providing more evidence that the effects of deprivation on the risk of stillbirth did not differ significantly between urban and rural births. To our knowledge, no other published analyses have estimated the risk for all of the standard categories of death from 24 weeks of gestation to 1 year of life and for a wide variety of causes of death.
Strengths and weaknesses of the study This was a large-scale study using data on births and deaths over a 7-year period from the 6376 enumeration districts in Wales which recorded births. We used data on deaths from the AWPS, a robust data set where complete ascertainment of deaths between 24 weeks of gestation and 1 year of life is accurately verified using records from the ONS and the Welsh Child Health System.
446 In this study, we used the ONS enumeration district classification.12 This is based upon a definition of land that is ‘irreversibly urban in character’ in the National Land Use Classification and is independent of administrative boundaries.14 An enumeration district was then defined as urban if the majority of its population resided in defined urban land within the enumeration district. All other enumeration districts were classified as rural. The classification of geographical areas into urban and rural has no agreed or standard definition. The literature describes a variety of approaches, including settlement size, population density, nearest neighbour, accessibility and multivariate area classification.15 Given the lack of consensus on a definition of rurality, it has been suggested that practical and sensible definitions appropriate for the particular study in question should be employed.2 Although the ONS classification based on land use is open to criticism for failing to acknowledge the wider social and economic differences that exist in rural areas,16 it was the most suitable for our study since we were able to model urban/rural status using a national definition at the smallest geographical level available, the enumeration district, to address the aims of this study. Since data on maternal socio-economic status are not systematically available for births in Wales, we used the Townsend score as the ecological adjustment for deprivation. There is an unresolved debate over the appropriateness of the use of deprivation indices in rural areas,2 since urbanbased deprivation indices may fail to identify pockets of deprivation in rural areas due to the dispersed and heterogeneous nature of rural populations.17 These indices include census variables that may be better proxies for low incomes in urban compared with rural populations. For example, the inclusion of the car ownership variable has been shown to be less valid for use in sparsely populated rural areas.18 In this study, exclusion of the car ownership variable from the Townsend score calculation recategorized rural enumeration districts as more deprived compared with the standard score. In our study, we have shown that the effect of the Townsend score on mortality rates before 1 year of age is not significantly different between rural and urban areas, so that the Townsend score can be used as a measure of deprivation for both rural and urban areas. Using the Townsend score rather than social class to adjust for deprivation raises the possibility of ecological bias.19 We would have preferred to model the data in a multilevel analysis20 to adjust for social deprivation at the individual level and estimate more precise parameter coefficients for urban/rural status at
Z.E.S. Guildea et al. the higher enumeration district level, but this was not possible without data on individual socioeconomic status. These results confirm our previous findings that social deprivation is significantly associated with several categories and causes of death under 1 year of age.7 Although the crude risk of death is lower in rural enumeration districts in Wales, we found no differences in this study between rural and urban enumeration districts after adjusting for deprivation. As we have argued previously,7 collaborative public health programmes to reduce individual and area-wide inequalities in the determinants of health are important. The results of this study suggest that it is necessary to tackle deprivation in rural areas as well as urban areas.
Acknowledgements We would like to thank the staff of All Wales Perinatal Survey for their assistance with the study.
Appendix Category of death
Definition
Therapeutic abortion
Therapeutic late fetal deaths before 24 weeks of gestation Spontaneous late fetal deaths before 24 weeks of gestation Late fetal deaths after 24 weeks of gestation Deaths occurring in the first 6 days of life Stillbirths and deaths in the first 6 days of life Deaths at 7–27 completed days of life Deaths in the first 27 completed days of life Deaths between 28 days and 1 year Deaths under 1 year of age (excluding stillbirths)
Spontaneous abortion Stillbirths Early neonatal Perinatal Late neonatal Neonatal Postneonatal Infant
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