Relation between parasuicide, suicide, psychiatric admissions, and socioeconomic deprivation

HOSPITAL ADMISSION DATA AND POPULATION DATA

We obtained details of patients aged over 10 and resident in the area covered by the Bristol and District Health Authority admitted after parasuicide between April 1990 and March 1994 from the South and West region's patient administration system (a routine health information system). We used the same system to identify patients aged 10-64 admitted under the specialty of mental illness over the same four year period. The patient administration system records patients' details, including date of birth, sex, and postcode, for all admissions to hospitals in the South and West region (formerly the South Western region). Each of the four main health care providers in the Bristol and District Health Authority is linked to the patient administration system, thus ensuring 100% coverage of all the authority's inpatient episodes. Patients resident in the area covered by the district health authority who are treated elsewhere in the region are similarly recorded and identifiable on the region-wide system. In all, 96.6% (5882/6089) of parasuicide admissions had a postcode for area of residence entered on the system. The number of district residents treated following parasuicide outside the region was small (94/6089 (1.5%)). All medical coders in the district are centrally trained and frequently audited. Senior coders meet every three months to discuss coding issues, which increases consistency between hospitals.

In the South and West region parasuicide admissions are identified by the codes E950-E959 (suicide and self inflicted injury) and E980-E989 (injuries undetermined whether accidentally or purposely inflicted) from the International Classification of Disease, ninth revision. We used this extended definition for parasuicide to ensure complete case ascertainment. Similarities in the age distributions for parasuicide coded as deliberate and for parasuicide coded as accidental overdose (E850-E859), except in elderly people, suggest that deliberate self poisoning is often coded as accidental. To overcome any variation in coding practices and to gain the most complete picture of parasuicide in the district we combined both these categories. Our figures may therefore slightly overestimate (by less than 5%) the true picture, particularly for older people, in whom accidental self poisoning is more likely. We did not include accidental injuries in this way. Wrist laceration coded as accidental is more likely to be truly accidental than is overdose coded as accidental, and inclusion of the former episodes may therefore distort the estimate of incidence. We omitted individuals aged 10 years or under from the analysis as intentional self harm in children is rare; self harm is most likely to be accidental.

To assess variations in event rates by small area we divided the district into 24 localities defined by postcode (mean population 34000) that were made up of aggregations of electoral wards to reflect natural communities. These had been previously identified and used for locality profiling by the district health authority (Bristol and District Health Authority's locality profiling notes, 1992). The population structure of these areas has changed little in the 13 years examined. Before considering correlations with deprivation, we investigated whether the observed differences between localities could have arisen by chance. Assuming a Poisson distribution, an approximateχ² test statistic is available15 since the standard used here is the district itself.

To assess person based admission rates, we linked separate episodes of care using district number, date of birth, and sex. Age and sex standardised parasuicide and psychiatric admission ratios for the district's residents, admitted to both psychiatric and general hospitals under the specialty of mental illness, were calculated by the indirect method of standardisation with 1991 census data from the Office of Population Censuses and Surveys for the Bristol and District Health Authority. Townsend scores were calculated for each of the localities from information collected in the 1991 census.16

SUICIDE DATA

Mortality data for 1982-91 were obtained from the Office of Population Censuses and Surveys' mortality files for Bristol and District Health Authority. These data covered a longer period of time to ensure there were sufficient events to produce standardised mortality ratios for each of the 24 localities of the district. There were on average 90-100 suicides a year in the district (ICD codes E950-E959, E980-E989). We included suicide and undetermined deaths as for parasuicide. Although there have been some changes in the population of Bristol over the 13 years covered by the morbidity and mortality data, comparison of 1986 mid-year population estimates with those of the 1991 census showed that there had been no significant changes between localities. Therefore the district population given by the 1991 census was again used as the standard population for calculating standardised mortality ratios.

STATISTICAL METHODS

Spearman's rank correlation coefficient was calculated to examine the relations between parasuicide, suicide, psychiatric admission, and deprivation. Nonparametric procedures were used to account for the effect of outlying values, which may exert a disproportionate influence on the strength of the relation observed with parametric statistics. We checked the age specific rates for parasuicide, psychiatric admissions, and deaths from suicide to ensure that the patterns are consistent with the summary standardised admission ratios and standardised mortality ratios. For all outcomes, for the age groups with adequate numbers of events, the age specific rank orders of the areas were practically identical to the rank order for the summary, though age groups for deaths from suicide had to be aggregated.

RELATIONS BETWEEN STANDARDISED ADMISSION RATIOS FOR PARASUICIDE, STANDARDISED MORTALITY RATIOS FOR SUICIDE, AND PSYCHIATRIC ADMISSION

Figures 3 and 4 show the relations between standardised admission ratios for parasuicide and standardised mortality ratio for suicide with standardised admission ratios for psychiatric admission. The correlation coefficient for standardised admission ratios for parasuicide with psychiatric admission rate was 0.76 (0.51 to 0.89). A similar relation between suicide and standardised admission ratios for psychiatric admission was found (0.72 (0.45 to 0.87)).

SUICIDE AND PARASUICIDE

A strong ecological relation exists between suicide and parasuicide; areas with high standardised mortality ratios for suicide also have high standardised admission ratios for parasuicide. This relation is present despite differences in the age-sex profile of the individuals committing the two acts and is partially explained by socioeconomic deprivation. The increased risk of suicide after parasuicide is recognised5; this phenomenon is unlikely to account, however, for the observed relation as less than 10% of individuals committing parasuicide go on to commit suicide.

SOCIOECONOMIC DEPRIVATION AND MENTAL ILLNESS

A strong ecological relation was also found between suicide and parasuicide (both well accepted indicators of psychiatric morbidity) and psychiatric admission rates in individuals aged 10-64. Hence psychiatric admission rates may reflect levels of psychiatric morbidity as indicated by parasuicide and suicide rates. The relation between parasuicide and one indicator of socioeconomic deprivation (unemployment) was documented in the early 1980s17 with both individual and ecological analyses. In Bristol a similar relation was found between unemployment and psychiatric admission rates in the 1990s14 and between parasuicide and deprivation in the 1970s.18 Rises in unemployment do not necessarily lead to rises in suicide,19 though we confirm a strong relation between suicide, parasuicide, and socioeconomic deprivation in the 1990s. Although raised standardised mortality ratios for suicide are found in social class I as well as class V and unemployed individuals, the relatively small number of cases of suicide in social class I leads to little impact on the standardised mortality ratio for suicide for locality.20

LIMITATIONS OF ADMISSION DATA FOR PARASUICIDE

Only individuals admitted after attending hospital for parasuicide are included here. In the Bristol District Health Authority about 63% of patients attending accident and emergency departments are admitted after parasuicide (Gunnell et al, unpublished data). The incidence of parasuicide after which the individual does not attend accident and emergency departments in the Bristol district is unknown. In addition, systematic differences may exist between hospital admission policies for parasuicide and the sociodemographic characteristics of catchment areas. This is unlikely, however, since the four hospitals in the Bristol district cover the observed range in Townsend scores and parasuicide admission ratios (fig 1). Systematic differences in the way general practitioners treat parasuicide in better off areas may also account for some of the observed differences, though this probably does not greatly confound the observed correlations.

THE ECOLOGICAL FALLACY

Ecological relations do not imply causation and have three main limitations. Firstly, we did not obtain indices of socioeconomic deprivation for individuals admitted to hospital or committing suicide. Individuals may not share the socioeconomic characteristics of the area population (the ecological fallacy). Secondly, those with mental illness may be differentially attracted to areas of deprivation by the availability of hostels and local authority housing as well as by the anonymity of life there.21 22 This is less likely to be the case with parasuicide than with severe mental illnesses such as schizophrenia. Lastly, underenumeration at the census--that is, disproportionately high underestimation of the population denominator in the more deprived areas--is a possible explanation.23 No information was available by locality to allow for this, and average underenumeration for districts is thought to be small (less than 1%). Moreover, this should have particular influence on young people, and, as stated, the relations between standardised mortality ratio and standardised admission ratio and deprivation are similar in all age groups.

Despite these reservations the relations between socioeconomic deprivation and health are well documented.24 For example, if the whole population experienced the same death rates as the non-manual classes an estimated 17000 fewer deaths would occur among 20-64 year old men.25 The close link between suicide and parasuicide shown here may be more noticeable now because of the increases in suicide among young men. For young men the factors associated with the rise in suicide may also be associated with rises in parasuicide. In the absence of effective interventions to prevent suicide and parasuicide, social policy changes aimed at decreasing socioeconomic deprivation may be more effective in reducing the incidence of acts. The Health of the Nation, however, did not include such targets.

CONCLUSIONS

These data and previous research support two conclusions. Firstly, the importance of socioeconomic deprivation as an indicator and possible determinant of psychiatric morbidity and suicide is clearly demonstrated. From these and other data, social policy and government measures to reduce socioeconomic deprivation may be as important in realising the Health of the Nation targets for suicide as health service activities. Such measures may also affect other indices of psychiatric ill health. Secondly, although suicide and parasuicide differ in several respects, the ecological relation between these acts suggests that they share to some extent a common cause and that this cause is largely related to socioeconomic deprivation.