Abstract
Cannabis is the most widely used illicit drug in developed countries, and has a significant impact on mental and physical health in the general population. Although the evaluation of levels of substance use is difficult, a method such as the randomized response technique (RRT), which includes both a personal component and an assurance of confidentiality, provides a combination which can achieve a considerable degree of accuracy. Various RRT surveys have been conducted to measure the prevalence of drug use, but to date no studies have been made of the effectiveness of this approach in surveys with respect to quantitative variables related to drug use. This paper describes a probabilistic, stratified sample of 1146 university students asking sensitive quantitative questions about cannabis use in Spanish universities, conducted using the RRT. On comparing the results of the direct question (DQ) survey and those of the randomized response (RR) survey, we find that the number of cannabis cigarettes consumed during the past year (DQ = 3, RR = 17 approximately), and the number of days when consumption took place (DQ = 1, RR = 7) are much higher with RRT. The advantages of RRT, reported previously and corroborated in our study, make it a useful method for investigating cannabis use. Copyright © 2016 John Wiley & Sons, Ltd.