Volunteer bias in nonrandomized evaluations of the efficacy of needle-exchange programs

• Published in: Journal of urban health Vol. 77; no. 1; pp. 103 - 112
• Main Authors: Hagan, Holly, McGough, James P., Thiede, Hanne, Hopkins, Sharon G., Weiss, Noel S., Alexander, E. Russell
• Format: Journal Article
• Language: English
• Published: United States Springer Nature B.V 01.03.2000; Springer-Verlag
• Subjects: Adult; Analysis of Variance; Cohort Studies; Confounding Factors (Epidemiology); Demography; Drug use; Evaluation Studies as Topic; Female; Homelessness; Humans; Interviews as Topic; Male; Needle exchange programs; Needle Sharing; Needle-Exchange Programs - standards; Observer Variation; Original : Various Topics; Socioeconomic Factors; Substance Abuse, Intravenous - psychology; Syringes; Washington; Washington; INE, USA, Washington, Seattle
• ISSN: 1099-3460; 1468-2869
• DOI: 10.1007/BF02350966

Nonrandomized comparisons of the incidence of HIV and hepatitis B and C between injection drug users (IDUs) who do and do not attend voluntary needle-exchange programs may be subject to bias. To explore possible sources of bias, we examined characteristics associated with voluntarily beginning or ceasing to participate in the Seattle needle exchange. In a cohort of 2,879 IDUs, a standardized questionnaire measured characteristics present at enrollment. We examined the relation of these characteristics to the proportion of IDUs who began to use the program during the ensuing 12-month follow-up period and to the proportion of current exchangers who dropped out during that period of time. Of the 494 never-exchangers at baseline, 32% attended the exchange program during follow-up; those who reported sharing syringes or who were homeless at enrollment were more likely to become new exchange users (adjusted risk ratio [ARR] for becoming an exchange user = 1.8 for those who shared syringes, and ARR = 2.2 for those who were homeless). Of 1,274 current exchangers, 16% stopped using the exchange during followup, with daily injectors (ARR = 0.6) and those who reported backloading (ARR = 0.6) being relatively less likely to drop out of the exchange. The analysis suggests that IDUs participating in needle-exchange programs at a given point in time may include a particularly high proportion of those injectors whose pattern of drug use puts them at elevated risk of blood-borne viral infections.