Journal of Public Health Advance Access originally published online on March 10, 2006
Journal of Public Health 2006 28(2):111-115; doi:10.1093/pubmed/fdi079
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Emergency call work-load, deprivation and population density: an investigation into ambulance services across England
Philip J. Peacock, Fourth year Medical Student1
Janet L. Peacock, Professor of Health Statistics2
1 University of Bristol, Bristol, UK
2 School of Health Sciences and Social Care, Brunel University, London, UK
Address correspondence to Janet L. Peacock, E-mail: janet.peacock{at}brunel.ac.uk
Demand for emergency ambulance services has risen steeply over the recent years. This study examined differences in work-load of ambulance services across England and investigated factors linked to high demand. The number of emergency calls received by each ambulance service in 1997 and 2002 and population and area data were used to calculate call rates and population density for each of 27 service areas. Deprivation score and proportion of the population under age 15 and over age 65 were calculated for each service area. There was wide variation in emergency call rates across England, with London having the highest rate both in 1997 (125.6 calls per 1000 persons) and in 2002 (140.1 per 1000). Statistically significant positive associations were observed between call rates and deprivation (1997, r = 0.49; 2002, r = 0.53) and between call rates and population density (1997, r = 0.70; 2002, r = 0.68). Following multivariable regression, the effect of deprivation score was consistently weaker, but the effect of population density was virtually unchanged. We conclude that areas with higher population density have higher call rates, which is not explained by deprivation. Deprivation is associated with higher usage, but its effect is partly due to population density. There is no evidence that these relationships are confounded by age.
Keywords: ambulances, population, emergency medical services, deprivation
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Introduction |
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Department of Health (DH) statistics show that demand for emergency ambulance services has been increasing steeply in recent years.1 However, little has been published about factors linked to high service demand or about variations in demand across the country. Carlisle et al. found that the use of general practice and hospital accident and emergency services varied with deprivation,2 but their study did not examine ambulance services and only looked at one city, Nottingham. Wass and Zoltie reported that increased use of accident and emergency departments is disproportionately high among elderly patients.3
This article reports the findings of a study of ambulance service usage in England, which has investigated the effects of deprivation, population density and age distribution of the population.
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Methods |
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For each of the 32 ambulance services in England, the number of emergency calls received in 1997 and 2002 was obtained from the DH.1 These years were chosen because 2002 was the most recent year for which government ambulance data were available at the time the study was conducted and 1997 provided a comparison with data taken 5 years before. Using population and area data available from the Office for National Statistics (ONS)4,5 and information about each service’s coverage, the area and population served by each ambulance service were calculated. From these data, population densities and call rates were calculated for both 1997 and 2002. Deprivation scores for each service area were calculated by averaging the index of multiple deprivation (IMD) scores for each of the component districts and unitary authorities, weighted by the population. The IMD scores, obtained from ONS, were produced in 2000 and took into account six factors: income; employment; health and disability; education, skills and training; housing; and geographical access to services [http://www.statistics.gov.uk accessed February 2004]. A higher IMD score indicates greater deprivation.
In some cases, the division between two ambulance services cut across a district. As population data were not available below district level, in these instances, data from adjacent ambulance services were combined. In three cases, data from two ambulance services were merged together, and in one case, three adjacent services had to be combined. This gave 27 ambulance services to be analysed.
For both 1997 and 2002, the relationship between call rate and other variables was tested using Pearson’s correlation. For the correlation tests, the natural logarithm of the call rates was used, as this best fitted a Normal distribution. All variables that were significantly related to call rate were fed into a multivariable linear regression to attempt to disentangle the relationships.
Statistical analyses were performed using Stata version 7.
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Results |
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Call rates varied widely across the country (Tables 1 and 2). In 1997, London had the highest call rate (126 calls/1000 people per year) and Wiltshire had the lowest (38 calls/1000). In 2002, London was again the highest (140 calls/1000), with Hereford & Worcester having the lowest call rate (60 calls/1000 people). In both 1997 and 2002, London’s call rate was far higher than the service with the second highest rate.
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Table 3 summarizes the correlations between call rate and deprivation, population density and two age categories. Fig. 1 shows scatter plots of call rates by population density and deprivation. As London was a major outlier, correlations were repeated with this area excluded. There was a moderately strong positive correlation between call rate and deprivation for both 1997 and 2002 (r = 0.49 and 0.53 respectively). There was a stronger positive correlation with population density for both years (r = 0.70 and 0.68). These associations were slightly weaker when London was excluded from the analysis.
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For both years, there was a negative correlation between call rate and the proportion over age 65, but the relationship was weak and non-significant. The proportion under age 15 was positively related to call rate, but all correlations were weak and mostly non-significant (Table 3).
Table 4 summarizes the results of multiple regressions on call rate. Predictor variables were deprivation score and population density; age was not included in the models as it was non-significant in the unifactorial analyses. For the 1997 data, the relationship between call rate and deprivation was weaker (regression coefficient halved) and became non-significant (P = 0.06) after adjusting for population density, whereas the relationship with population density was hardly changed. A similar pattern was seen in 2002, with the relationship with deprivation becoming weaker after adjustment and that with population density not changing although both factors remained statistically significant.
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Discussion |
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Main finding of this study
This study has shown that there is considerable variation in call rates between areas and that London has a far higher call rate than any other area of the country. The variation in call rates is partly explained by deprivation and population density, which are both positively related to call rates. The effect of deprivation was partly due to the relationship with population density, but the effect of population density is not explained by deprivation. There is no evidence that these effects are confounded by differences in age distributions.
What is already known on this topic
Demand for ambulance services has increased substantially in recent years, with call rates doubling between 1989 and 1999 in London.6 Government statistics show that this trend is continuing.1 There is evidence that utilization of health services is linked to levels of deprivation.2
What this study adds
To our knowledge, there have been no studies of English ambulance services, which have investigated variation in demand across the country and factors related to the variability. This study explores and quantifies the variability in call rates across England at two time points, five years apart, and shows consistent positive relationships with deprivation and population density.
As ambulance services across England are faced with increasing demand for emergency ambulance services, it is important to know what factors are linked to high service demand. Further research is needed to investigate why people living in high population density areas and those with greater levels of deprivation are making greater use of ambulance services. A clear understanding of reasons for high usage of emergency ambulance services is necessary to best direct attempts to meet genuine needs and to reduce inappropriate usage of the English ambulance services.
Limitations of this study
This study has certain limitations. The call rates were not age standardized, as age-specific call data could not be obtained from either the DH or individual ambulance services. As a substitute, we used both the proportion of the population under 15 and proportion over 65 to investigate differences in age distribution between service areas. Since there was no evidence of a relationship between the age distribution and call rate, it is unlikely that the relationships between deprivation, population density and call rate are because of children or the elderly using services more.
Another limiting factor is that the call rates were based solely on the resident population in each area. The number of non-resident workers was not taken into account, a factor that could possibly explain London’s high call rate. However, previous research has shown that use of ambulance services in London has increased most outside of working hours, when non-resident workers would be unlikely to be service users.6
This study used available routine data in an ecological analysis investigating effects of deprivation and population density. However, these two factors only explained 56% of the total variability in call rates between areas, and hence a substantial proportion of the variability remained unexplained.
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Acknowledgements |
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This study was originally conducted to fulfil a ‘student selected component’ for the MBChB course at the University of Bristol.
We thank Professor Yoav Ben-Shlomo from the Department of Social Medicine at Bristol, for his help throughout the original project.
The authors declare there are no conflicts of interest.
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References |
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- Department of Health. Statistical bulletin 2003/13: Ambulance services, England: 2002–3. 2003. London.
- Carlisle R, Groom LM, Avery AJ, Boot D, Earwicker S. Relation of out of hours activity by general practice and accident and emergency services with deprivation in Nottingham: longitudinal survey. Br Med J 1998;316:520–3.
[Abstract/Free Full Text] - Wass A, Zoltie N. Changing patterns in accident and emergency attenders. J Accid Emerg Med 1996;13:269–71.[Abstract]
- Office for National Statistics. Mid-1997 Population Estimates; Quinary age groups and sex for health authorities in England and Wales; estimated resident population revised in light of results of the 2001 Census. 2002. London.
- Office for National Statistics. Mid-2002 Population Estimates; Quinary age groups and sex for health authorities in England and Wales. 2002. London.
- Peacock PJ, Peacock JL, Victor CR, Chazot C. Changes in the emergency workload of the London Ambulance Service between 1989 and 1999. Emerg Med J 2005;22:56–9.
[Abstract/Free Full Text]
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