The proportion of unemployment, disability pension and sick

Transcription

1 EUROPEAN JOURNAL OF PUBLIC HEALTH 2004; 14: European Public Health Association 2004; all rights reserved A population study of the association between hospitalization for alcoholism among employees in different socio-economic classes and the risk of mobility out of, or within, the workforce ANDERS ROMELSJÖ, MARLENE STENBACKA, MICHAEL LUNDBERG, MARIANNE UPMARK * Background: Alcohol problems can increase the risk of downward mobility within, or mobility out of, the workforce. The magnitude of this risk has been unclear, as has also been the question whether the risk is different for men and women, for different socio-economic classes, and for single-living compared with co-habiting people. Methods: The study period was , when unemployment was low in Sweden. Information about socio-economic status from censuses was linked to hospitalization for alcoholism, alcohol psychosis and alcohol intoxication (AAA) over the period in Stockholm County in persons aged years in 1970 and gainfully employed in the same socio-economic category in both 1970 and 1975, and to general population data. The standardized rate ratio for mobility out of the workforce and for downward socio-economic mobility was calculated for those hospitalized with AAA. Results: There was a statistically significant risk of mobility out of the workforce over the period in both sexes and in all socio-economic groups. The relative risk was 6.63 for male skilled and semi-skilled manual workers and 9.52 for non-manual employees at medium and high level, while the corresponding figures were lower for women. The absolute risk of leaving the workforce was lowest in non-manual employees at medium and high level. The relative risk was reduced in persons who were co-habiting. Conclusions: Severe alcohol problems are powerful determinants of downward mobility within, or mobility out of, the workforce in both sexes and in all socio-economic categories. Keywords: alcoholism, cohort, disability pension, marital status, social class, social mobility The proportion of unemployment, disability pension and sick leave is strongly increased among high consumers of alcohol / problem drinkers / alcohol abusers / alcohol-dependent persons (alcoholics), according to studies from Sweden and other countries Out of 467 men aged 60 years studied in a 1970s health survey in Uppsala 12% were on disability pension, and 30% of these had alcohol problems. 3 In a late 1970s health survey of all middle-aged men in Malmö, Sweden, Kristenson, Öhrn and Hood 11 found that the proportion of disability pensioners increased with increased level of the alcohol-related enzyme gamma-glutamyltransferase (GGT) in serum, as did the number of sick days over the previous 20 years. In a longitudinal population study Upmark, Möller and Romelsjö 9 found that both men and women with high alcohol consumption had a highly increased relative risk (RR) of being granted a disability pension within 7 years. Mullahy and Sindelar 7 in an analysis based on the US National Health Interview Survey, found that problem drinking results in increased unemployment for both men and women. Öjesjö 5 and Ågren and Romelsjö 12 report that alcoholism in Sweden is more common among people who are not gainfully employed. Finally, Romelsjö and Diderichsen 13 report that in a study in Stockholm County in-patient care for alcoholism was associated with downward mobility within the workforce. It is therefore obvious that alcohol-related problems can be a cause of mobility out of the workforce, leading to disability pension, unemployment or to downward socio-economic mobility. To our knowledge the risk of gainfully employed alcoholics in the population moving out of, or downwards within, the workforce has not been assessed in previous studies. Also, it is unclear whether there are differences between different socio-economic categories with regard to the probability for alcohol-related mobility out of or within the workforce. Such differences could contribute to the marked difference in the rate of alcohol-related problems between socio-economic categories (i.e. among those who do not show this kind of social mobility but remain in these categories). 12,17 Several studies report an increased prevalence of alcohol problems among the divorced or single compared with married or co-habiting persons. 6,11,12,18,19 Ågren and Romelsjö 12 report that in Sweden during the period mortality with an alcohol diagnosis was markedly elevated among divorced, single or widowed persons. Poikolainen 18 reports that the risk of alcohol-related hospitalization among 69,886 hospitalized men in Finland was predicted by social class and marital status. But the magnitude of the risk of married/co-habiting persons of becoming single does not seem to have been previously assessed in alcohol-dependent men and women from different social classes. There does not seem to have been a previous study to assess a presumed protective effect of co-habiting with regard to downward social mobility in these groups. Scientific knowledge is therefore lacking on whether the risk varies for alcohol-related mobility out of, or downwards within, the workforce among men and women, in different socioeconomic categories, and in co-habiting versus single-living persons. This paper investigates the role of severe alcohol problems, measured as hospitalization with an alcohol diagnosis, with regard to the probability of moving out of, or downwards * A. Romelsjö 1,2,3, M. Stenbacka 2,3,4, M. Lundberg 2, M. Upmark 2,5 1 Centre for Social Research on Alcohol and Other Drugs, Stockholm University, Stockholm, Sweden 2 Karolinska Institute, Department of Public Health Sciences, Stockholm, Sweden 3 Stockholm Addiction Centre, Magnus Huss Clinic, Karolinska Hospital, Stockholm, Sweden 4 Karolinska Institute, Department of Clinical Neuroscience, Stockholm, Sweden 5 Centre of Alcohol and Drug Prevention, Stockholm Public Health Centre, Stockholm, Sweden Correspondence: Professor Anders Romelsjö, Centre for Social Research on Alcohol and Other Drugs, Stockholm University, Stockholm, Sweden, tel , fax , anders.romelsjo@sorad.su.se 53

2 EUROPEAN JOURNAL OF PUBLIC HEALTH VOL NO. 1 within, the workforce. The probability for gainfully employed, co-habiting alcoholics to become single, and the question whether co-habiting has a protective effect is also analysed. The study has a longitudinal design, with the subjects being followed over a 10-year period. The study s objectives were therefore to: estimate the risk among gainfully employed men and women in different socio-economic categories hospitalized with alcoholism, alcohol psychosis and alcohol intoxication ( AAA diagnoses ) of subsequent mobility out of, or downwards within, the workforce; study the risk for co-habiting or married employed subjects hospitalized with an AAA diagnosis of becoming single; and estimate whether gainfully employed alcoholics who are cohabiting/married are at reduced risk of social mobility out of the labour market. MATERIALS AND METHODS Data collection for this study was done during a period in Sweden characterized by a fairly stable labour market, with less than 3% unemployment 20 and a well-established social welfare system. The study period was chosen because of the stability and low unemployment in the labour market at the time. In the early 1990s the labour market in Sweden became unstable and unemployment increased. A study of data from the 1990s would have led to greater difficulties in interpreting the results also owing to great changes in eligibility criteria for a disability pension. 10 The study is based on an analysis of a register containing information from three population censuses and of data on hospitalization and mortality in Stockholm County. Census data on occupation and marital status in 1970, 1975 and 1980 for individuals were linked to information about hospitalization with selected diseases in the computerized Stockholm County In-Patient Care Register (ICR) during the period by use of the unique individual Swedish personal identification number. The participation in each of the three censuses was over 99%. The percentage of discharges reported in the ICR rose successively from 92% in 1970 to more than 97% in 1973 and has been above 98% since The diagnoses were recorded according to the Swedish edition of the Manual on the International Classification of Diseases, Injuries and Causes of Death, 8th revision (ICD-8), 21,22 during the study period. The study population consisted of all men and women in Stockholm County aged years in 1970 and employed in the same socio-economic category in 1970 and in 1975, who were hospitalized at least once during the period with an AAA diagnosis as main or contributory diagnosis. Altogether 1234 men and 345 women met the inclusion criteria. The socio-economic categories, based on the Swedish socioeconomic classification (referred to hereafter by its Swedish term SEI were: unskilled or semi-skilled manual (blue-collar) workers, skilled manual (blue-collar) workers, non-manual employees at a low level (low-level white-collar workers), non-manual employees at medium or high level (medium and high level white-collar workers) including self-employed professionals and entrepreneurs. 23 By choosing subjects with an occupation in the same socio-economic category in the censuses of both 1970 and 1975 groups with a fairly stable socio-economic status were selected. Separate analyses were made of those subjects in this cohort who were co-habiting both in 1970 and in During the 5-year period between the 1975 census and the 1980 census some subjects left the workforce or changed to another main socio-economic category. Those who left the workforce comprised persons who became unemployed, became students, or had not worked during 1980 owing to illness, or who had become disability pensioners or housewives or househusbands. Disability pensioners and persons on sick leave due to illness probably constitute the majority. Another data set was used, comprising a 10% random sample of all male and female census participants aged years in Stockholm County in 1970, employed in the same socio-economic category in both 1970 and This information was used to calculate rates of gainfully employed persons in the same socio-economic category who were hospitalized with an AAA diagnosis during the period , and of the whole population, for the following events: leaving the workforce between 1975 and 1980; moving downwards from a higher to a lower SEI category; and of those co-habiting in 1970 and in 1975, but single in Less than 3% of the adult population in the county were hospitalized with an AAA diagnosis during the period , according to calculations based on data from the ICR. The data were age- and sex-standardized with the direct method, using the age distribution for both sexes in 1975 as weights. Age-standardized rate ratios (SRR), a measure of relative risk RR, 24 were calculated for both men and women for mobility out of, or downwards within, the workforce between the census of 1975 and that of The SRR was set to 1.00 for all men and women who were gainfully employed in the same main socioeconomic category during both 1970 and 1975 and who in 1970 were aged years, according to the 10% random sample of the census population. 95% confidence intervals were also calculated. Similar calculations were done to compare the risk for downward social mobility for co-habiting with that for single persons. RESULTS Hospitalization with an AAA diagnosis during the period was associated with a markedly, statistically significantly increased probability for mobility out of the workforce between 1975 and 1980, for both sexes and all socio-economic categories, but more for men than for women (table 1). The SRRs varied between 6.63 and 9.84 in men. The SRRs among women were Table 1 Standardized rate ratio (SRR) a and 95% confidence interval (95% CI) for mobility out of the workforce during period for gainfully employed men and women aged years in 1970 and hospitalized during period for alcoholism, alcohol intoxication or alcohol psychosis Unskilled and semi-skilled workers, 1970 and 1975 (n=427 men and 128 women) Skilled workers, 1970 and 1975 (n=410 men and 18 women) Non-manual low-level employees, 1970 and 1975 (n=124 men and 151 women) and 1975 (n=265 men and 47 women) a: SRR=1.00 for mobility out of the workforce during period for gainfully employed men and women in the general population who were in the same socio-economic category in both 1970 and 1975.

3 Alcoholism and social mobility lower, but the variation between socio-economic categories was greater, with a SRR of 1.60 among skilled and semi-skilled women and a SRR of 6.70 among non-manual employees at low level. The SRR for the eight self-employed men was 8.20 (95% CI: ), while there was only one such case among women. Table 2 provides information about the absolute risk of mobility out of the workforce and shows that in both sexes a greater proportion of manual than non-manual employees left the workforce, especially compared with non-manual employees at medium and high level. Only 40 men and 13 women hospitalized with an AAA diagnosis moved downwards within the workforce (table 3). Much fewer, in other words, than the number of men and women who moved out of the workforce (table 1). The SRR for downward mobility, or a downward drift, within the workforce was generally increased (table 3), but it was lower than for mobility out of the workforce (table 1). The risk was statistically significant in the two categories of male nonmanual employees. The SRR for co-habiting persons hospitalized with AAA in of becoming single between 1975 and 1980 was 3.32 (95% CI: ) among men and 3.31 (95% CI: ) among women. Table 4 shows that persons in the study population who were co-habiting in both 1970 and 1975 had a reduced risk for mobility out of the workforce, compared with those who were not co-habiting. This reduction in risk was greater in female unskilled and semi-skilled workers and in non-manual workers employed at a low level than it was in the corresponding categories in men. The SRR decrease was statistically significant among female non-manual employees at low level and also, in the category of male non-manual employees at medium and high, including self-employed professionals. DISCUSSION In 1987 Månsson and Israelsson 25 in a study of 5950 middle-aged men found a clearly increased mean level of the alcohol-related enzyme GGT of 1.32 microkatal/litre among 123 employed men who 4 8 years later became disability pensioners, compared with 0.81 microkatal/litre among all participants. Some of the subjects were probably severe alcohol abusers, others not. The finding of these authors showing that high alcohol consumption is associated with mobility out of the labour market, 25 is consistent with our findings in a group of subjects with advanced alcohol problems, but does not provide information about social class or women. Romelsjö and Diderichsen 13 report that 34% of men and 29% of women aged years (ages slightly different from those in this study) in 1976 and hospitalized for an AAA diagnosis during 1981 in Stockholm County had left the workforce during the preceding 5 years. The lower percentages, about 24%, in our study may be linked to the selection of subjects. Our subjects had a certain socio-economic stability, since they were in the same socio-economic category in both 1975 and Table 1 shows that the risk of mobility out of the workforce was lower among women than among men in all socio-economic categories. This can be explained at least in part by differences in the labour market, with an increased demand, especially for women, in the workforce during the study period. The employment rate among women in Sweden increased considerably between 1970 and 1980, while the same trend did not occur among men. It is also possible that female alcohol-dependent subjects went for treatment at an earlier stage than alcoholdependent men did. However, our study showed a markedly increased probability also for employed women with an alcohol diagnosis to leave the workforce. Table 2 shows the absolute risk in different socio-economic categories of leaving the workforce. Subjects hospitalized with an AAA diagnosis were at higher absolute risk of moving out of the labour market if they were manual workers than if they were non-manual employees. This supports the commonly held view that alcoholism is more easily compatible with work among non-manual employees than among manual workers. One explanation for this is that tolerance among employers and work Table 2 Percentage and 95% confidence interval (95% CI) of subjects aged years in 1970, who were hospitalized during period with a diagnosis of alcoholism, alcohol intoxication or alcohol psychosis, who were gainfully employed in the same socio-economic category in both 1970 and 1975 and who left the workforce between 1975 and 1980 Total Socio-economic category Percentage (95% CI) Percentage (95% CI) Percentage (95% CI) Unskilled and semi-skilled workers (n=427 men and 128 women) 24.3 ( ) 29.7 ( ) 25.6 ( ) Skilled workers (n=410 men and 18 women) 31.2 ( ) 27.8 ( ) 31.1 ( ) Non-manual, low-level employees (n=124 men and 151 women) 23.4 ( ) 22.5 ( ) 22.9 ( ) Non-manual, middle- and high-level employees, and self-employed professionals (n=265 men and 47 women) 14.7 ( ) 10.6 ( ) 14.1 ( ) Average 24.5 ( ) 23.7 ( ) 24.3 ( ) Table 3 Standardized rate ratio (SRR) a and 95% confidence interval (CI) for mobility downwards within the workforce during period for gainfully employed men and women aged years in 1970 who were hospitalized during period with alcoholism, alcohol intoxication or alcohol psychosis Non-manual low-level employees, 1970 and 1975, manual workers, 1980 (n=14 men and 7 women) and 1975, manual workers, and 1975, low-level non-manual employees, 1980 (n=13 men and 3 women) a: SRR=1.00 for mobility downwards in the workforce during period for gainfully employed men and women in the general population who were in the same socio-economic category in both 1970 and

4 EUROPEAN JOURNAL OF PUBLIC HEALTH VOL NO. 1 mates for employed with severe alcohol problems (i.e. workers hospitalized with an AAA diagnosis) may vary from occupation to occupation and, therefore, among different SEI categories. The observed social gradient may also reflect the higher risk of economic inactivity for persons with long-standing illness, an effect found to be modified by socio-economic position, with a higher risk for lower socio-economic groups. 26 Variation in demand between occupations may also contribute to differences in the probability of mobility out of the workforce. In their review Martin, Roman and Blum 27 found that the following conditions could explain an increase in likelihood of alcoholism in different occupations: placement in stressful or non-rewarding jobs, participation in job-based drinking networks and absence of work-based social support. The same kind of factors may also contribute to increasing the likelihood of mobility out of the workforce. Information about these factors in our dataset was lacking. One must be aware that our results may not be entirely valid for socio-economic categories in general, as our cohort consisted of persons who had remained in the same socio-economic category at two times, 5 years apart. However, the great majority of job changes in the general population are between jobs of the same or a similar kind in the same socio-economic category, which increases the generalizability of the findings. 20 Differences between occupational categories in rate of mobility out of the labour market (an ongoing process) also have an influence on social class differences in rates of alcohol-related hospitalization (among those who remain in the labour market). Downward mobility from the non-manual to the manual socioeconomic category contributes to higher rates of alcohol-related hospitalization among manual workers. In our study this effect was limited owing to the low number of subjects (table 3). Possibly downward mobility in some cases is one step in the process of leaving the workforce. The net effect of this kind of social mobility is an increase in the rate of measures of severe alcohol problems (hospitalization and mortality, for instance) among manual workers. The present study also shows that severe alcohol problems are associated with an increased risk of separation among cohabiting men and women in the general population. This is in agreement with data from other studies. 12,28 Table 4 indicates that co-habiting may give some protection from mobility out of the workforce among those with prior hospitalization with an AAA diagnosis, and that this effect can also vary by sex and socio-economic category. This interpretation is supported by an overwhelming amount of literature on the protective effect of social support. 29 Co-habiting persons have the possibility of receiving support from a spouse or partner. For instance, when a new drinking period starts, a spouse may help or encourage the drinker to seek treatment. On the other hand, a large proportion of female alcohol abusers live with male alcohol abusers. It is possible that the alcohol problems were generally less severe among the married or co-habiting subjects in our study population, as some of these may have been brought to treatment comparatively earlier by worried partners. A comparatively large proportion of unmarried persons may have undergone separation mainly due to their severe alcohol habits. Strengths and weaknesses of the study There are certain inherent weaknesses in our data set, which should be mentioned here. We had no information about eventual differences in alcohol use, degree of dependence and other risk factors for social mobility in our subjects from different socio-economic categories. We could not separate the different sub-components (i.e. unemployed, disability pensioners, long-standing illness, and housewives, househusbands, students) in the endpoint mobility out of the workforce, and therefore could not analyse whether the associations are different for the different categories of this endpoint. A strength of the data set is that it included almost all cases of alcoholism in the population. At the only private hospital in Stockholm there was hardly any in-patient care of subjects with an AAA diagnosis during the study period. Studies based on self-reports in surveys have a varying degree of non-participation, generally with an increased proportion of heavy consumers among the non-participants, not least according to Swedish data The incidence of being on disability pension was higher among non-participants in a health screening survey for middle-aged men, 34 as was alcohol dependence as a cause for a disability pension (23.2% compared with 7.3% among participants). This raises the question of a selection bias of survey data, both with regard to exposure and with regard to confounders and it also reduces the precision of the estimates of alcohol-related problems. 24 A case control study among subjects hospitalized with an AAA diagnosis utilizing self-reports of different kinds of relevant conditions as well as a physical examination and information from records would give a deeper understanding of risk factors and causality in the complex processes of leaving the labour force. The study was supported by grant No. 92:0300:4C from the Swedish Council for Social Research. We would like to thank Maria Danielsson and Finn Diderichsen for their valuable advice. REFERENCES 1 Pell S, D Alonzo CA. Sickness absenteeism of alcoholics. J Occup Med 1970;12: Medhus A. Alcohol problems among male disability pensioners. Scand J Soc Med 1976;4: Waern U. Findings at a health survey of 60-year-old men Table 4 Standardized rate ratio (SRR) a and 95% confidence interval (CI) for mobility out of the workforce during period for co-habiting compared with single-living men and women aged years in 1970, who were gainfully employed in the same socio-economic category in both 1970 and 1975 and hospitalized during period with alcoholism, alcohol intoxication or alcohol psychosis Unskilled and semi-skilled workers Skilled workers Non-manual low-level employees Non-manual medium and high-level employees, and self-employed professionals a: SRR=1.00 for mobility downwards in the workforce during period for gainfully employed men and women in the general population who were in the same socio-economic category in both 1970 and 1975.

5 Alcoholism and social mobility and recorded disease during their preceding 10 years of life [Dissertation]. Uppsala, Sweden: Acta Universitatis Upsaliensis, Dahlgren L, Ideström CM. Female alcoholics: V. Morbidity. Acta Psychiat Scand 1979;60: Öjesjö L. The relationship to alcoholism of occupation, class and employment. J Occup Med 1980;22: Damström-Thakker K. Long-term utilization of medical and social services in a population of clinical alcoholics [Dissertation]. Stockholm, Sweden: Karolinska Institute, Mullahy J, Sindelar J. Employment, unemployment, and problem drinking. J Health Econ 1996;15; Upmark M, Romelsjö A, Hemmingson T, Lundberg I. Alcohol use, social factors and early retirement: a cohort study of 50,000 young Swedish men. Eur J Public Health 1997;7: Upmark M, Möller J, Romelsjö A. Longitudinal, population-based study of self-reported alcohol habits, high levels of sickness absence, and disability pensions. J Epidemiol Community Health 1999;53: Upmark M. Alcohol, sickness absence, and disability pension: a study in the field of disease, ill health, psychosocial factors, and medicalisation [Dissertation]. Stockholm, Sweden: Karolinska Institute, Kristenson H, Öhrn J, Hood B. Convictions for drunkenness or drunken driving, sick absenteeism, and morbidity in middle-aged males with different levels of serum-glutamyltransferase. Prev Med 1982;11: Ågren G, Romelsjö A. Mortality in alcohol-related diseases in Sweden during in relation to occupation, marital status and citizenship in Scand J Soc Med 1992;20: Romelsjö A, Diderichsen A. Changes in alcohol-related in-patient care in Stockholm county in relation to socio-economic status during a period of decline in alcohol consumption. Am J Public Health 1989;79: Whitehead PC, Simpkins J. Occupational factors in alcoholism. In: Kissin B, Begleiter K, editors. The pathogenesis of alcoholism: psychosocial factors. Volume 6, pp New York, NY: Plenum Press, Romelsjö A, Lundberg M. The changes in the social class distribution of moderate and high alcohol consumption and of alcohol-related disabilities over time in Stockholm county and in Sweden. Addiction 1996;91: Hemmingsson T, Lundberg I, Diderichsen F. The roles of social class of origin, achieved social class and intergenerational social mobility in explaining social-class inequalities in alcoholism among young men. Soc Sci Med 1999;8: Mäkelä P. Alcohol-related mortality as a function of socio-economic status. Addiction 1999;94: Poikolainen K. Risk of alcohol-related hospital admission in men as predicted by marital status and social class. J Stud Alcohol 1982;44: Thundahl KL, Allebeck P. Abuse and dependence on alcohol in Swedish women: role of education, occupation and family structure. Soc Psychiatr Epidemiol 1998;9: Statistiska Centralbyrån (Statistics Sweden). Arbetsmarknaden (The labour market ). Stockholm, Sweden: Statistiska Centralbyrån, World Health Organisation. Manual on the international statistical classification of diseases, injuries and causes of death. 8 th rev. ed. Geneva, Switzerland: World Health Organisation, Socialstyrelsen (The Swedish National Board of Health and Welfare). Klassifikation av sjukdomar mm (Classification of diseases, etc.). Stockholm, Sweden: Socialstyrelsen, Statistiska Centralbyrån (Statistics Sweden). Svensk socio-ekonomisk indelning (Swedish socio-economic classification). Stockholm, Sweden: Statistiska Centralbyrån, Rothman K, Greenland S. Modern Epidemiology. Boston, MA: Lippincott, Månsson NO, Israelsson B. Middle-aged men before and after disability pension. Scand J Soc Med 1987;15: Lindholm C, Burström B, Diderichsen F. Class differences in the social consequences of illness? J Epidemiol Community Health 2002;56: Martin JK, Roman PM, Blum TC. Job stress, drinking networks, and social support at work: a comprehensive model of employees problem drinking behaviors. Sociol Quart 1996;37: Steinglass P, Robertson A. The alcoholic family. In: Kissin B, Begleiter K, editors. The pathogenesis of alcoholism: psychosocial factors. Volume 6, pp New York, NY: Plenum Press, Berkman L, Glass T. Social integration, social networks, social support and health. In: Berkman L, Kawachi I. Social epidemiology. Oxford: Oxford University Press, 2000: Nilsson T, Svensson PG. Alcohol habits and attitudes: RUS (The national study). In: The alcohol habits of the Swedish people. Report from the Government Commission on Alcohol Policy. Stockholm, Sweden: Ministry of Finance, (SOU 1971:77). (In Swedish.) The drinking habits in the Swedish population: the national survey in Kristenson H. Studies on alcohol-related disabilities in a medical intervention programme in middle-aged males [Dissertation]. Malmö, Sweden: Lund University, Romelsjö A. The relationship between alcohol consumption and social status in Stockholm: has the social pattern of alcohol consumption changed? Int J Epidemiol 1989;18: Rosengren A. Coronary heart disease and mortality in relation to alcohol abuse and social factors: 10,000 men aged years in Gothenburg, followed over 11.8 years [Dissertation]. Göteborg, Sweden: Göteborg University, Månsson NO, Råstam L, Eriksson KF, Israelsson B, Melander M. Incidence of and reasons for disability pension in a Swedish cohort of middle-aged men. Eur J Public Health 1994;4:22-6. Received 24 October 2001, accepted 13 November