AIDS, Sexual Behavior, and Intravenous Drug Use (1989) / Chapter Skim
Currently Skimming:
On the Accuracy of Current Estimates of the Numbers of Intravenous Drug Users
On the Accuracy of Current Estimates of the Numbers of Intravenous Drug Users
Pages 429-446
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From page 429... ...
to the Domestic Policy Council.i The purpose is not to develop alternative estimates but rather to see whether the published estimates are accurate enough to be relied upon for estimating and forecasting the extent of human immunodeficiency virus (HIV) infection.
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Uncler one interpretation, the "relative frequency" (RF) interpretation, the estimate X is viewed as a realization of a stochastic process; for example, if X is based on the results of randomly selected samples, then the randomization inherent in the sampling gives rise to a probability distribution for X (i.e., different samples would give rise to different estimates of X)
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believes that, at least in some communities such as Baltimore, "approximately 20%0 of IVDUs are primary cocaine and amphetamine users who (lo not on a regular basis abuse opioirls intravenously." Many varieties of patterns of needle use exist. Some persons inject drugs subcutaneously ("skin poppers")
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Thus, if Rj is the seropositivity rate for group j and if Nj is the size of group j, the total number of infected persons in the population is Rat Nit + R2N2 + R3N3 + R4N4 + · · + R8Ns, . If group 4 were split into two groups, say 4a and 4b, with rates R4a and R4b and sizes N4a and N4b, then the total number of infected persons in the population may be expressed as:
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TABLE 1 Public Health Service (1986, 1987) Estimates of HIV Prevalence Among IV Drug Users Type of IV Drug User Estimated Approximate Total Number Number Seroprevalence (%)
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He noted that many "drug treatment professionals report that IV drug users more likely to be infected with HIV (i.e., engage in more risky behaviors) tend not to seek treatment at drug centers where HIV testing is known to occur but prefer programs in which there is not testing." However, the extent of the avoidance of such treatment programs depends on how much real choice a user has of treatment program and whether testing is optional.
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As shown in the following section, the population definitions used for estimates of numbers of {VDUs are exceedingly vague regarding frequency of injection. How exactly were the seroprevaTence estimates developed for each state and how were the differences between seroprevaTence rates for regular and occasional users estimated?
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The extent of bias in the survey results is unknown but potentially enormous.2 Back-extrapolation methods use data on AIDS deaths and HIV 2For example, the decennial census is believed to miss as many as 15 percent of all black males aged 20-44; the percentage of IVDUs missed by the census is surely much higher. If 30 percent of the drug abusers are not covered by the census, and if only one in two drug abusers surveyed would admit being a drug abuser, then the number of drug abusers reported by the survey will tend to be only 35 percent of the actual number.
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Problems include errors in classifying individuals as to membership on one list 3Newmeyer also describes a variation on this method in his unpublished note "Four Readily Applicable Methods to Estimate Drug Abuse Prevalence" (personal communication, 1988~: The method is to ascertain from the medical examiner's "coroner's] toxicology data the relative proportion of decedents with methadone metabolites to decedents with heroin metabolites (metabolite is simply a chemical produced by the body's metabolism of a drug.)
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states provided data on the total number of IV drug abusers in the State.4 The highest estimates of IV drug abusers were provided by New York, California, and Texas, in that order.... States were also asked to report the basis for their estimates of 4The following states were excluded: Alabama, Alaska, Arizona, Arkansas, Colorado, Delaware, District of Columbia, Florida, Georgia, Hawaii, Idaho, Indiana, Kansas, Kentucky, Louisiana, Maine, Montana, Nebraska, Nevada, New Mexico, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Puerto Rico, South Carolina, South Dakota, Tennessee, Utah, Vermont, Virginia, Virgin Islands, Washington, West Virginia, and Wyoming.
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If the state plan estimates for the other 33 states, Puerto Rico, the District of Columbia, and the Virgin Islands are included, the total increases to 1.447 million. The national estimates described above can be no better than the state estimates they are based on.
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Data from DAWN and the California Drug Abuse Data System (CALDADS) as well as "street data" were used to estimate the fraction of drug abusers who administered the drugs intravenously; the estimates were subjectively adjusted downward slightly to account for selection bias.
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In brief, the past estimates were based on regression estimation using drug indicators as predictors, and the regression models were estimated by using a combination of Narcotics Registry and clual-systems estimates. The method is complicated because some of the predictor variables became unavailable and had to be predicted on the basis of other, available indicators.
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. Then regression models were fitted to predict smoothest successive differences of logs of 1970-1974 numbers of heroin acIdicts from the first principal component.
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500,000. (These ratios may be interpreted as number of IVDUs in cities in a given size range divided by total population in those 7The source for this is an unauthored, undated document "Estimated Number of IV Drug Abusers in U.S." The estimated number of heroin addicts in 1982 is taken from Shreckengost (1983~; estimates for the number of heroin IV users who are not addicts and the number of users of IV drugs other than heroin and cocaine are supplied by NIDA; the estimate of the number of cocaine heavy users was reported in the 1985 National Household Survey on Drug Abuse.
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Newmeyer's Ratio Estimate John Newmeyer recently developed a method for estimating the number of {VDUs in Standarc] Metropolitan Statistical Areas (SMSAs)
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. One could attempt to improve the method by using principal components of several indicators or a multivariate ratio estimator, but the critical dependence on items (1)
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(1987) Estimates of Numbers of IV Drug Users Infected with HIV: Preliminary Data.
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