23. ROAD INJURIES AND DEATHS INDICATOR
TABLE 1 – INDICATOR DESCRIPTION
| Information component | Pg 4 Health Summary – Indicator No 23 |
| Subject category / domain(s) | How long we live and what we die of |
| Indicator name (* Indicator title in health profile) | People killed or seriously injured on the road (*Road injuries and deaths) |
| PHO with lead responsibility | SWPHO |
| Date of PHO dataset creation | Feb 2007 |
| Indicator definition | People killed or seriously injured on the roads of the area, Crude rate per 100,000 resident population, All ages, 2003-2005, |
| Geography | England, GOR, Local Authority: Counties, County Districts, Metropolitan County Districts, Unitary Authorities, London Boroughs |
| Timeliness | The indicator presented in Health Profiles is not routinely updated but may become available in future Health Profiles. The rates and numerators published by DfT are available annually (usually October-December). |
| Rationale:What this indicator purports to measure | Unintentional deaths and serious injuries on public roads caused by road traffic collisions |
| Rationale:Public Health Importance | Motor vehicle traffic accidents are a major cause of preventable deaths and morbidity, particularly in younger age groups. For children and for men aged 20-64 years, mortality rates for motor vehicle traffic accidents are higher in lower socioeconomic groups. For instance, there would be 600 fewer deaths in men aged 20-64 years from motor vehicle traffic accidents each year if all men had the same death rates as those in social classes I and II combined. (Acheson D. Report of the Independent Inquiry into Inequalities in Health. London: TSO, 1998.Department of Health. The NHS Plan. London: TSO). The vast majority of road traffic collisions are preventable and can be avoided through improved education, awareness, road infrastructure and vehicle safety (Peden M, Scurfield R, Sleet D, Mohan D, Hyder AA, Jarawan E et al. 2004, World report on road traffic injury prevention. Geneva: World Health Organisation). |
| Rationale: Purpose behind the inclusion of the indicator | To help reduce road injury and death. |
| Rationale:Policy relevance | One of the Department of Transport’s PSA targets is to reduce the number of people killed or seriously injured by 40%, and the number of children killed or seriously injured by 50% by 2010 compared with the baseline of 1994-8. In Saving Lives: Our Healthier Nation, ‘accidents’, including road traffic collisions, were identified as one of the four main priority areas. Tackling Health inequalities: A programme for action included a headline target to reduce road casualty numbers in disadvantaged areas . |
| Interpretation: What a high / low level of indicator value means | A high indicator value (red circle in health summary chart) represents a statistically significant higher rate of road injury and death when compared to the national value. A low indicator value (amber circle in health summary chart) represents a statistically significant rate of road injury and death when compared to the national value.However, as the vast majority of road traffic collisions are preventable, any number of deaths and injuries greater than 0 is undesirable and therefore a low indicator value should not mean that PH action is not needed.Factors that should be considered when interpreting this indicator include the nature of the road network, volumes of traffic and number of pedestrians. |
| Interpretation: Potential for error due to type of measurement method | Research has shown that not all road casualties are reported to police. Therefore, this indicator may be an under-estimate of the true level of serious injury. Districts with low resident populations but which have high inflows of people or traffic may have artefactually high rates because the at-risk resident population is not an accurate measure of exposure to transport. This is likely to affect employment centres and sparsely populated rural areas which have high numbers of visitors or through traffic. |
| Interpretation: Potential for error due to bias and confounding | The completeness of reporting road injury to the police has been shown to vary by factors such as age, injury severity and type of road user. For example, research suggests that cyclists are less likely to report injury to the police. There are also differences by age group, with higher reporting rates amongst younger and older people. Age also impacts on injury severity, with older people more likely to be seriously injured or killed when involved in a road collision. Therefore, population structure and mix of traffic in areas may contribute to variation in Local Authority values. |
| Confidence Intervals: Definition and purpose | A confidence interval is a range of values that is normally used to describe the uncertainty around a point estimate of a quantity, for example, a mortality rate. This uncertainty arises as factors influencing the indicator are subject to chance occurrences that are inherent in the world around us. These occurrences result in random fluctuations in the indicator value between different areas and time periods. In the case of indicators based on a sample of the population, uncertainty also arises from random differences between the sample and the population itself.The stated value should therefore be considered as only an estimate of the true or ‘underlying’ value. Confidence intervals quantify the uncertainty in this estimate and, generally speaking, describe how much different the point estimate could have been if the underlying conditions stayed the same, but chance had led to a different set of data. The wider is the confidence interval the greater is the uncertainty in the estimate.Confidence intervals are given with a stated probability level. In Health Profiles 2007 this is 95%, and so we say that there is a 95% probability that the interval covers the true value. The use of 95% is arbitrary but is conventional practice in medicine and public health. The confidence intervals have also been used to make comparisons against the national value. For this purpose the national value has been treated as an exact reference value rather than as an estimate and, under these conditions, the interval can be used to test whether the value is statistically significantly different to the national. If the interval includes the national value, the difference is not statistically significant and the value is shown on the health summary chart with a white symbol. If the interval does not include the national value, the difference is statistically significant and the value is shown on the health summary chart with a red or amber symbol depending on whether it is worse or better than the national value respectively. |
TABLE 2 – INDICATOR SPECIFICATION
| Indicator definition: Variable | People killed or seriously injured on the roads of the area |
| Indicator definition: Statistic | Crude rate |
| Indicator definition: Gender | Persons |
| Indicator definition: age group | All ages |
| Indicator definition: period | Numerator 2003 – 2005, Denominator mid-2004 |
| Indicator definition: scale | Per 100,000 resident population |
| Geography: geographies available for this indicator from other providers | England, GOR, Local Authority: Counties, Unitary Authorities, London BoroughsAnnual rates and numerators available for these geographies from www.dft.gov.uk |
| Dimensions of inequality: subgroup analyses of this dataset available from other providers | Numerator data is available from www.dft.gov.uk for Counties, Unitary Authorities, London Boroughs broken down by age group and road user type. |
| Data extraction: Source | Department for Transport |
| Data extraction: source URL | http://www.dft.gov.uk/pgr/statistics/datatablespublications/accidents/casualtieslatables/ |
| Data extraction: date | Data extracted from source as at: 8/12/2007 |
| Numerator: definition | 3-year average of the number of people (all ages) killed or seriously injured on the roads of a LA in the period 2003-05The indicator is based on casualties who incur injury on the public highway (including footways) in which at least one road vehicle or a vehicle in collision with a pedestrian is involved and which becomes known to the police within 30 days of its occurrence. The vehicle need not be moving and accidents involving stationary vehicles and pedestrians or other road users are included. One accident may give rise to more than one casualty.This indicator includes only on casualties who are fatally or seriously injured and these categories are defined as follows. Fatal casualties are those who sustained injuries which caused death less than 30 days after the accident; confirmed suicides are excluded. Seriously injured casualties are those who sustained an injury for which they are detained in hospital as an in-patient, or any of the following injuries, whether or not they are admitted to hospital:fractures, concussion, internal injuries, crushings, burns (excluding friction burns), severe cuts and lacerations, severe general shock requiring medical treatment and injuries causing death 30 or more days after the accident. A casualty is recorded as seriously or slightly injured by the police on the basis of information available within a short time of the accident. This generally will not reflect the results of a medical examination, but may be influenced according to whether the casualty is hospitalised or not. Hospitalisation procedures will vary regionally. |
| Numerator: source | Department for Transport |
| Denominator: definition | 2001 Census based mid-year population estimate for the mid-point year (2004)Data are based on the latest revisions of ONS mid-year population estimates for the respective year, current as at 24 August 2006. |
| Denominator: source | Office for National Statistics (ONS). |
| Data quality: Accuracy and completeness | Coverage is complete. Data quality varies as there are differences between police forces in procedures for recording, collecting and collating. There is no information available about the extent of this variation. Serious injury is not recorded on the basis of a clinical diagnosis. This may cause problems in classification of serious versus slight injury. Other sources of data which measure road injury and death are death registrations data (which matches well with police reports of road deaths) and hospital episode statistics. The match between hospital admissions and police reports of serious injury is discussed comprehensively in recent national reports: http://www.dft.gov.uk/pgr/roadsafety/research/rsrr/theme5/underreportingofroadcasualti4788http://www.dft.gov.uk/pgr/roadsafety/research/rsrr/theme5/roadaccidentscasualtiescompa4787There are differences between police data and hospital records of road casualties due to differences in both definitions and reporting. |
TABLE 3 – INDICATOR TECHNICAL METHODS
| Numerator: extraction | Downloaded from www.dft.gov.uk |
| Numerator: aggregation /allocation | Calculated a 3-year average for 2003-2005 by summing the individual years and dividing by 3. |
| Numerator data caveats | Research has shown that not all road casualties are reported to police. DfT published two papers on the level of under-reporting on 23 June 2006, which can be found at the addresses below: http://www.dft.gov.uk/pgr/roadsafety/research/rsrr/theme5/underreportingofroadcasualti4788http://www.dft.gov.uk/pgr/roadsafety/research/rsrr/theme5/roadaccidentscasualtiescompa4787These reports suggest that the serious group of casualties could be up to twice as large as indicated by the ‘serious’ category in police records.. Not all of this shortfall in the serious group of casualties is due to under-reporting because in the slight category are casualties which should be in the serious category and have been misclassified or misrecorded. These could add up to another 25% to the serious category.The police definition of ‘serious’ injury has remained consistent and therefore this data can be used to look at time trends. However, it should be noted that recording practices may have changed over time. An alternative to using casualties and deaths occurring on the roads in the area would have been to use a measure of resident casualties and deaths, regardless of where they occurred, using hospital admissions data. This would be a good measure of the health effects upon the population which lives in the district but would be less useful for targeting of road safety interventions. For this reason, occurring casualties and deaths were used in the Health Profiles. |
| Denominator data caveats | Ideally, the denominator should include all people travelling on public roads in the area (in vehicles and as pedestrians) and take account of the distances travelled. This measure is not available. The use of resident population as a denominator is a proxy measure for population exposure and is consistent with how this indicator is presented elsewhere. |
| Methods used to calculate indicator value | Calculation of the numerator: Calculated a 3-year average for 2003-2005 by summing the individual years and dividing by 3. Denominator count: Mid-2004 population estimates (all ages). The numerator was then divided by the denominator; the resulting value was then multiplied by 100,000 to give a crude rate per 100,000 population. |
| Small Populations: How Isles of Scilly and City of London populations have been dealt with | Any casualties recorded on the Isles of Scilly are included in the Cornwall numerator, consistent with how this data is published by DfT. Therefore the Isles of Scilly population is included in the Cornwall denominator.The City of London counts (numerator and denominator) are included in the London regional total. |
| Disclosure Control | Not applicable as no counts less than 5. |
| Confidence Intervals calculation method | The confidence intervals for these crude rates were constructed using the following formula that relates the chi-square and Poisson distributions: where LL and UL are lower and upper confidence limits respectively for the rate as d events per unit time exposed, χ² ν,a is the (100*α)th chi-square centile with ν degrees of freedom, and d is the number of observed events (e.g. serious injuries and deaths). Reference:Dobson AJ, Kuulasmaa K, Eberle E, Scherer J. Confidence intervals for weighted sums of Poisson parameters. Statistics in Medicine 1991;10:457-462. |
Posted in: Indicators