The reliability of drug use indicators collected from a prisoner sample using the life events calendar method

Abstract

Some methods of retrospective data collection are known to produce reliable indicators of drug use, but the Life Event Calendar (LEC) method has not been convincingly tested. As well, previous assessments of reliability typically focus on treatment program participants or others that are not representative of criminally active populations, and address one or two substances and time frames ranging from just a few days to twelve months. Our aim is to address those gaps by examining the test-retest reliability of self-reported drug use among prisoners across a wider variety of substances and over a longer reference period than previous research. Accordingly, we analyzed data that were collected using the LEC method during 2005–2007 from a random sample of 110 minimum and medium security prisoners. Drug use over an eighteen month period preceding the arrest that led to their imprisonment was conveyed. On average, the main or first interview (test) was completed 162.4 days (SD = 62.47) following prison admission, and the retest occurred three weeks following the main interview (test). Reliability is assessed using gamma and kappa. Self-reported drug use was reliable across a variety of substances, although reliability did vary. Reliability was stronger among African American, more highly educated, and older subjects. Yet, self-reported drug use among white, less educated, and younger subjects was acceptably reliable. Considering the lengthy lag between admission and first interview, this study provides strong evidence that the LEC method is suitable to collect reliable self-reported data on multiple forms of drug use from prisoners.