Feasibility and validity of low-budget telephonic follow-up interviews in routine outcome monitoring of substance abuse treatment

Aims   Routine outcome monitoring (ROM) is receiving growing attention. However, follow-up interviews are time-consuming and costly. This study examines the feasibility and validity of low-budget telephonic follow-up interviews for ROM in a substance abuse treatment centre (SATC).
Design   Observational study using data collected for routine outcome monitoring.
Setting   The study was performed in a SATC in an urban area in the Netherlands.
Participants   Feasibility and validity were assessed on data of 2325 patients.
Measurements   Data on pre-treatment socio-demographic and clinical characteristics were collected using electronic patient records (EPRs) and the European version of the Addiction Severity Index (EuropASI). Data on intensity of treatment were also collected through the EPRs. Telephonic follow-up interviews were conducted between 9 and 10 months after intake.
Findings   A 53% follow-up rate was achieved; 35% of the patients could not be contacted, 3% explicitly refused and in 8% other reasons accounted for non-participation. About 50% of the interviews took place in the intended time-frame. Costs were €40 ($57) per completed interview. There were indications of selection bias, because patients with cocaine as their primary problem and patients with polysubstance abuse were under-represented in the follow-up sample; the presence of these disorders is associated with negative treatment outcome.
Conclusions   Implementing telephonic low-budget follow-up interviews for ROM is feasible, but selection bias threatens internal validity of data, limiting generalization to the total treatment population. Increased efforts to track patients for follow-up may improve generalization.