Scottish Centre for Infection and Environmental Health, Glasgow
Medical Research Council Biostatistics Unit, Cambridge
Scottish Centre for Infection and Environmental Health, Glasgow
Scottish Centre for Infection and Environmental Health, Glasgow
Department of Medicines Management, Keele University, Staffordshire
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1 The 1994 interview asked "how much money do you spend on drugs in an
average day?"; the response was scaled up to weekly drug expenditure for
comparison with 1993 data. The change in recording of drug expenditure was
introduced for the 1994 survey because of the difficulty found by respondents
in calculating expenditures on a weekly basis.
Correspondence: S. J. Hutchinson, Scottish Centre for Infection and Environmental Health, Clifton House, Clifton Place, Glasgow G3 7LN
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ABSTRACT |
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Aims To investigate factors associated with drugs expenditure and to estimate the cost of illegal acquisitions used to pay for drugs.
Method We collected self-report data from 954 current injectors, interviewed at multiple street, needle/syringe exchange and drug treatment sites throughout Glasgow.
Results Injectors' mean weekly drug spending was £324. The mean annual illegal drugs spend was estimated to be £11 000 per injector. We provide a central estimate - £194 million per annum - of the retail value of goods acquired illegally by injectors in Glasgow in order to pay for drugs. Higher drug spends were associated with having been imprisoned more often and with those reporting acquisitive crime, drug dealing and prostitution. Treatment with methadone, among individuals who injected in the previous two months, was associated with a 20% reduction in a typical spend on drugs.
Conclusions Treatment effectiveness needs to be measured both in terms of health benefit and in terms of reduction in drugs expenditure and recidivism.
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INTRODUCTION |
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METHOD |
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Subjects
An IDU was defined as someone who had injected drugs in the previous two
months. In order to reduce the effect of treatment for drug use on current
risk behaviours, respondents recruited from in-treatment sites were only
eligible for participation if their current episode of treatment had begun
within the previous four weeks.
Statistical analyses and outcome measures
The 1993 and 1994 interviews were the first to ask questions about income
from legal and illegal sources and about expenditure on drugs; a total of 1024
IDUs were interviewed in these years. Respondents were asked the following:
(a) "how much money do you spend on drugs in an average
week?"1; (b)
"how much money do you get from all sources in an average week?";
and (c) "thinking about all the money you had to live on during the past
six months, what proportion has come from illegal sources?". IDUs with a
total income of more than £7000 in an average week (four cases, all of
whom reported drug dealing as their main source of illegal income) or less
than £10 per week (11 cases) were evidently outliers, and were omitted
from analysis on the grounds that these values would seriously distort
estimates such as mean values. (It has been suggested that drug dealers tend
to self-report revenue from drug sales rather than net financial
profit (Bretteville-Jensen & Sutton,
1996); this may have caused the large values for incomes.) Drug
spending data were missing for a further 55 IDUs and so analyses were
performed on responses from 954 individuals.
Sample characteristics for these 954 individuals are shown in Table 1. We summarised injectors' weekly drug expenditure and total income as follows. The illegal yield of respondents in an average week is obtained by multiplying the answers to Questions (b) and (c): this product divided by the answer to Question (a) is the estimate of the proportion of drug expenditure obtained illegally. The product of four variables - (i) the mean weekly drug expenditure of respondents, (ii) the estimated proportion of the drug expenditure that was obtained illegally, (iii) the estimated prevalence of injecting drug use in Glasgow (Frischer et al, 1993b) and (iv) a factor to account for periods of abstinence from drug use in a year - provides an estimate of the annual illegal drug expenditure of injectors in Glasgow. A further multiplier is then applied to this figure so as to estimate the value of goods acquired illegally in order to pay for drugs.
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We were interested in how much injectors spend on drugs in relation to demographic details, drug use intensity, treatment utilisation and crime. Preliminary analyses involved collapsing continuous and ordinal variables into groups according to either examples of categories used in previous studies or empirical examination of the distribution of continuous variables, which yielded a natural cut-off. Mean and median drug expenditures are reported for the key variables, and the Kruskal-Wallis rank sum test was used to compare drug expenditures between groups.
Ordinary least-squares regression was then used to investigate these factors in association with reported spend on drugs. A multiple linear regression model including all key variables is specified. On the basis of the multiple regression analyses, we provide an estimate of the impact of methadone treatment on drug expenditure of individuals who had injected drugs in the previous two months, while controlling for potential confounders. The response variable (drug spend in an average week) and age first injected drugs had skewed continuous distributions and were therefore transformed (on a natural logarithm scale, as used in previous studies, such as Healey et al (1998b)) in order to induce normality and to stabilise variances in the regression residuals. Highly skewed continuous data (namely number of times imprisoned and frequency of injecting drugs) were categorised for the purpose of the regression analyses in order to reduce the influence of extreme scores. The residuals of the multiple regression model were studied graphically (Armitage & Berry, 1994) - in a normal quantile plot, against the predicted values and against the predictor variables - in order to assess how well the model explains the data (plots available from authors on request). Cook's distance (Cook, 1977) was also calculated in order to detect cases which overly influenced the regression coefficients. All analyses were conducted using the S-PLUS software package (MathSoft, 1997).
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RESULTS |
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The drug most frequently used was heroin; 90% (856/954) of respondents had used it in the six months prior to interview. Most participants (97%, 923/954) reported using more than one drug during the previous six months. Almost half of the participants (48%, 455/952) reported using opiates, benzodiazepines and stimulants in the previous six months, while 37% (352/952) had used opiates and benzodiazepines (but not stimulants), 5% (44/952) had used opiates and stimulants (but not benzodiazepines) and 10% (98/952) had used only opiates in the previous six months (another three had only used either benzodiazepines or stimulants; there were two non-responses).
One-fifth of participants (190/940) had no illegal source of income in the six months prior to being interviewed. Sixty-nine per cent (514/750) of participants who had an illegal source of income reported that their main source was acquisitive crime, which includes all types of theft.
Fifty-eight per cent (553/954) of respondents had received treatment (including drug-free counselling, residual rehabilitation or maintenance or detoxification with methadone or other drugs) in the previous month. The questionnaire does not ask how long these respondents had been receiving treatment for their drug use; but owing to the nature of the inclusion criteria for individuals recruited from in-treatment settings, at least 44% (246/553) had begun their treatment within the previous month.
Drug expenditure and proportion from illegal sources
Mean weekly drug expenditure of the 954 injectors was £324 (s.e.=9.6,
median £250, range £10-£2660). Mean weekly income from all
sources was £422 (s.e.=13.5, median £300). The mean illegal yield
of participants was, coincidently, £324 per week (s.e.=12.5, median
£235, range £0-£4000), and the mean percentage of drug
expenditure from illegal sources was then estimated to be 71% (s.e.=1.3%),
with a median of 93% (inter-quartile range 51-100%).
Annual cost of illegal acquisitions used to pay for drugs
A recent study of terms of imprisonment in the period 1983-94 in Saughton
Prison for 316 male injectors who were in the Edinburgh City Hospital HIV
cohort showed that they spent approximately six weeks of each year in prison
(Seaman et al, 1998).
On the basis of these data and the assumption that half of imprisoned
injectors continue to inject inside prison at a reduced frequency of six times
per month (Bird et al,
1997), we shall assume that injectors spend four weeks on average
not purchasing drugs per annum. Their mean illegal spend on drugs would
therefore be (mean weekly drug spend x percentage of drug spend illegal
x number of drugs purchasing weeks) £324 x 0.71 x 48
£11 000 per IDU per annum. Hence, in Glasgow, with an estimated
8500 current IDUs (Frischer et
al, 1993b), the amount of illegally acquired money
being spent on drugs annually by injectors is estimated at £94
million.
The black-market value of stolen goods is low - between a quarter and a half of the retail value (Dougal, 1999, personal communication). Hence, for an injector whose illegal income is mainly generated through acquisitive crime, an illegal drugs spend of £11 000 per annum could require the acquisition of goods with a retail value of between £22 000 and £44 000 (central estimate £33 000).
Sixty-nine per cent of respondents with an illegal income reported acquisitive crime as their main source in the previous six months (see Table 1). The extent to which those individuals reporting acquisitive crime as their main source supplement their illegal income in part by non-acquisitive crime cannot be estimated from this study. A question which directly measures the amount of illegal income associated with acquisitive crime needs to be developed. However, in the absence of such a measure, an indirect estimate of 69% is used here as a proxy for the proportion of illegal drug expenditure obtained from acquisitive crime on any one day. Hence, the annual cost of illegal acquisitions used to pay for drugs among injectors in Glasgow could range from £129 million to £259 million (£22 000 x 0.69 x 8500 to £44 000 x 0.69 x 8500), with a central estimate of £194 million (£33 000 x 0.69 x 8500).
Variations in drug expenditure
Table 1 provides summary
statistics of weekly drug expenditure in relation to characteristics of the
injector group, including demographic details, drug use intensity, treatment
utilisation and crime. The mean drug spend was significantly but slightly
higher among those interviewed in 1994 (£336) than among those
interviewed in 1993 (£312); this could be explained by the change in the
subject of the question from weekly expenditure in 1993 to daily expenditure
in 1994. Drug expenditure was higher among those recruited at treatment and
street settings than among those recruited at needle exchanges. Younger
individuals, respondents with longer injecting careers and those commencing
injecting drug use at an earlier age tended to have higher expenditures.
Participants who had received only methadone treatment in the previous month had significantly lower drugs spends than those who had received no treatment for their drug use. Those imprisoned (overnight or for longer) more times since first injecting drugs and those who had ever injected inside prison had significantly higher drug spends. Those who reported no illegal income in the previous six months had lower drugs expenditures (mean £116, s.e.=9.3) than those reporting mainly acquisitive crime (mean £336, s.e.=9.6), drug dealing (£497, s.e.=49.9) or prostitution (£533, s.e.=39.3).
Frequency of injecting drugs, whether opiates, benzodiazepines or stimulants, was related to increased drug expenditures. Those who preferred other drugs to heroin particularly buprinorphine, dihydrocodeine or methadone, but not temazepam, had lower drugs expenditures.
Multiple linear regression analyses: factors associated with drug
expenditure
Table 1 shows the factors
significantly associated with drug expenditure, including year of interview,
recruitment setting, gender, age when drugs first injected, receiving only
methadone treatment in the previous month, number of times in prison since
starting to inject drugs, main source of illegal income (acquisitive crime,
drug dealing or prostitution), frequency of injecting opiates and preferred
drug. The multiple regression model including these factors was able to
explain 50% of the observed variation in drug expenditure on natural log
scale. The model was significant, and graphical study of the residuals showed
no obvious pattern, suggesting no outlying points or variance heterogeneity,
and gave no reason to doubt that the residuals were normally distributed.
Multi-collinearity between explanatory variables was not a problem.
Examination of Cook's distance showed that no cases exerted undue influence on
the regression coefficients.
Adjusting for other significant determinants of drug expenditure, participants who had received only methadone treatment for their drug use in the previous month (owing to the nature of the inclusion criteria, at least 18% (23/127) of these would have begun their methadone treatment during that month) had a mean reduction of 0.22 (s.e.=0.08) in the natural logarithm of drugs spend, from 5.56 (the intercept of the multiple regression model) to 5.34 - approximately a 20% reduction in median spend from £260 to £209 in an average week after back-transformation.
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DISCUSSION |
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In the period 1990-94, around 500 IDUs were recruited annually by our research team into studies of HIV prevalence, risk behaviours and lifestyle. The team's credibility with Glasgow injectors was therefore well established before questions about illegal income and drug expenditure were introduced in 1993. Findings have been reproducible between years (Taylor, 1993) and corroborated by data generated in other investigations (Gore & Bird, 1995). The validity of these results relies on participating IDUs' self-report data (Brown et al, 1992). In particular, biases may exist as a result of respondents under-reporting criminal activity, although studies of the behaviour of drug users have found no significant problems with the accuracy of self-reported criminal histories (Parker et al, 1998). Although we are unable to test the validity of the interview data, corroboration by external findings (detailed below) makes the drugs expenditure data from this reputedly difficult-to-access group arresting, and much needed - as the Task Force to Review Services for Drug Misusers (1996) highlighted.
Self-reported drugs expenditure
Our finding of a mean weekly drug spend by Glasgow injectors of £324
(s.e.=9.6) is remarkably close to the average of £307 per week estimated
for 466 new service users at the Possilpark Drugs Project in Glasgow in the
two years up to December 1992 (Meikle, 1998, personal communication). More
recently Edmunds et al
(1996) estimated drug
expenditure at £333 per week for 191 users interviewed in London. Half
of the Glasgow injectors interviewed in the present study reported that 93% or
more of their drugs spend was from illegal sources; the mean was 71% from
illegal sources.
Cost of illegal acquisitions used to pay for drugs
Our central estimate of the retail value (£194 million per annum) of
goods acquired illegally by injectors in Glasgow in order to pay for drugs
assumed that 69% of illegal expenditure is financed through acquisitive crime.
This assumption contrasts with the results of a study conducted in Oslo which
interviewed 900 drug injectors attending needle-exchange services and
concluded that theft accounted for 23% of total drugs expenditure, while the
corresponding figures for drug dealing and prostitution were 42% and 21%
respectively (Bretteville-Jensen &
Sutton, 1996). However, it was also noted by the authors of that
report that Oslo opiate users generate a larger proportion of their income
through drug sales than do Scottish users, and it was reasoned that
differential drug prices or potential profitability of this income source may
cause the differences between countries in the relative contribution of
dealing activity to drug users' income.
The central retail value estimate of £194 million does not include earnings from crimes such as prostitution or drug dealing. In addition to the above illegal acquisition costs, there are law enforcement and criminal justice costs (Task Force to Review Services for Drug Misusers, 1996), medical costs (Taylor et al, 1996) and social costs (Healey, 1998b) of injecting drug use, which were beyond the scope of this analysis but which are as important as the acquisition costs. While our sample is likely to be representative of the injector population in Glasgow, the estimates should not be generalised to the wider drug-taking population of non-injectors.
Factors associated with reported spend on drugs
Higher weekly drug spends were associated with respondents who had been
imprisoned more often and with those reporting acquisitive crime (55% of
respondents, 514/940), drug dealing (11%, 108/940) and prostitution (20% of
female injectors, 57/288). Starting to inject at an earlier age was associated
with higher drug expenditures. Drug expenditure increased significantly with
the frequency of injecting opiates and decreased for those who preferred
buprenorphine (preferred by 11%, 107/954), dihydrocodeine (5%, 48/954) and
methadone (3%, 31/954) by comparison with those preferring heroin (56%,
531/954).
Impact of methadone treatment on drugs expenditure
After adjustment for the significant factors mentioned above, methadone
treatment during the previous month was associated with a 20% reduction in
typical drugs spend. This reduction is almost certainly a minimum estimate,
because only current injectors - individuals who had injected in the previous
two months - were eligible for entry into the study. As a result, persons who
had been prescribed methadone and who were not injecting, or were only
injecting infrequently, would not have been included. In addition, individuals
recruited from in-treatment settings were only eligible to participate if they
had begun their current episode of treatment for drug use in the previous four
weeks; however, this only applied to 18% of the methadone group, so the
majority of this sample were actually recruited outwith in-treatment settings
and as such could have been receiving methadone for longer than four
weeks.
The Task Force to Review Services for Drug Misusers (1996) regarded the lack of UK research on drug treatment effectiveness as its largest single handicap. It therefore initiated an observational study (the National Treatment Outcome Research Study) and, more pointedly, called for randomised controlled trials of drug treatment effectiveness (Gore & Seaman, 1996). While we accept that a more rigorous appraisal of methadone treatment effectiveness is required, the regression analysis in this paper, in the current absence of better data, yields a conservative estimate of the impact of this intervention on drug expenditure.
While this study clearly demonstrates a positive relationship between crime and drug expenditure, at an individual level a reduction in drug expenditure may not necessarily lead to a reduction in illegal activity. For some, drug use is simply an extension of a pre-existing deviant lifestyle (Healey, 1998a). For others, the difficulty in generating sufficient income to support desired consumption and a close relationship with the criminal underworld may provoke and encourage criminal behaviour (Jarvis & Parker, 1989; Deschenes et al, 1991). Cohort and cross-sectional studies are in progress in Glasgow, aimed at assessing, specifically and comprehensively, the impact of methadone prescribing on key outcomes, including drugs expenditure and illegal sources of income (details available from author on request). Early results suggest that the effect of methadone treatment on drugs expenditure is more dramatic than the 20% reduction that we have posited from this epidemiological study, and that large reductions in acquisitive crime have taken place.
While methadone alone was shown to be associated with a reduction in drug expenditure, we were unable to assess specifically in this study, owing to a lack of numbers and to the inclusion criteria, whether other treatments (e.g. residential rehabilitation or drug-free counselling) are also associated with such reductions. Randomised trials are therefore needed in order to measure treatment effectiveness and the effectiveness of alternative interventions both in terms of health benefit to individuals and in terms of reduction in drugs expenditure and recidivism.
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Clinical Implications and Limitations |
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LIMITATIONS
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REFERENCES |
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Received for publication December 14, 1998. Revision received June 30, 1999. Accepted for publication June 30, 1999.
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