Research Article Following Up Crack Users after Hospital Discharge Using Record Linkage Methodology: An Alternative to Find Hidden Populations Veralice Maria Gonçalves, 1,2 Rosemeri Pedroso, 1 Antônio Marcos dos Santos, 2 Lisia Von Diemen, 1 and Flavio Pechansky 1 1 Center for Drug and Alcohol Research, Clinics Hospital of Porto Alegre, Federal University of Rio Grande do Sul, 400 Professor Alvaro Alvim Street, 90420-020 Porto Alegre, RS, Brazil 2 Information Technology Department of the Unifed Health System, National Ministry of Health, Brazil Correspondence should be addressed to Veralice Maria Gonc ¸alves; veralice@terra.com.br Received 7 May 2015; Accepted 4 August 2015 Academic Editor: Handan Wand Copyright © 2015 Veralice Maria Gonc ¸alves et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis paper presents the probabilistic record linkage (PRL) methodology as an alternative way to fnd or follow up hard-to-reach population as crack users. PRL was based on secondary data from public health information systems and the strategy used from standardization; phonetic encoding and the rounds of matching data were described. A total of 293 patient records from medical database and two administrative datasets obtained from Ministry of Health Information Systems were used. Patient information from the medical database was the identifers to the administrative datasets containing data on outpatient treatment and hospital admissions. 40% of patient records were found in the hospital database and 12% were found in the outpatient database; 95% of the patients were hospitalized up to 5 times, and only 10 out of them had outpatient information. Te record linkage methodology by linking government databases may help to address research questions about the path of patients in the care network without spending time and fnancial resources with primary data collection. 1. Introduction In 2012, about 3.5 to 7.0 percent of the world population aged between 15 and 64 had used an illegal drug at least once in a previous year [1]. In the Americas, the most prevalent primary drug of abuse among those seeking treatment was cocaine [1]. In Brazil, crack-cocaine consumption has become more prominent; however, treatment of this specifc type of drug use remains a challenge [2, 3]. Longitudinal follow- up studies about this type of drug use ofen cannot fnd these patients at the appropriate level of retention and there are too many losses, since they seem to evade afer hospital discharge. Attempts to follow up this hidden and hard-to-reach population for evaluating the efectiveness of interventions face methodological difculties. Furthermore, longitudinal studies and clinical trials are conducted at very high costs. One option to overcome these limitations is to utilize another method for evaluating interventions: the record linkage methodology based on secondary data available from the existing information systems. Record linkage techniques based on medical and admin- istrative databases have been used on epidemiological studies in several countries. Tese studies generally involve the use of hospital, population, and outpatient data, which allow for the collection of comprehensive patient information and for more robust analyses [4, 5]. Retrospective cohort studies have been employed in Canada [4], Australia [6], and the United States [7], as well as in a number of European and Scandina- vian countries [8], to investigate issues such as cause-specifc mortality [9], hospital admissions [10], prevalence of mental disorders [11], and antecedents of deliberate self-harm [12]. Record linkage (RL) studies involve the comparison of data in medical and administrative databases with the aim of fnding records that are believed to relate to the same Hindawi Publishing Corporation BioMed Research International Volume 2015, Article ID 973857, 5 pages http://dx.doi.org/10.1155/2015/973857