BACKGROUND: Daily diary measurements are a common way to assess substance use behaviours, however researchers and clinicians are often cognizant of assessment reactivity (or “reactivity”) in daily substance use measurement. Reactivity involves changes to behaviours that result simply from self-monitoring those behaviours. When reactivity to substance use measurement has been found to exist, it has been identified both as a possible confound in daily diary research and a potential intervention tool in clinical practice. Reactivity to daily self-monitoring of alcohol and tobacco use has been investigated in prior research, however this research has been inconsistent. Reactivity to daily self-monitoring of cannabis use quantity has yet to be documented at all. METHOD: The current study involved secondary analyses of data from N=88 women who self-monitored their cannabis use for 32 consecutive days (Joyce et al., under review). We examined objective reactivity of cannabis use to daily self-monitoring both for the probability of use each day as well as the quantity of cannabis used on each cannabis-using day. At study completion, participants were asked the degree to which they felt self-monitoring impacted their cannabis use (i.e., subjective reactivity). We explored the reported degree of subjective reactivity, and we examined correspondence between objective and subjective reactivity. RESULTS: Hurdle models were the best fit for the data. Participants’ probability of daily cannabis use and the quantity of cannabis use did not change significantly over the study period. For subjective reactivity, many respondents (45%) reported no subjective reactivity, though a majority (55%) reported some degree of subjective reactivity with 24% reporting moderate or more reactivity. A three-step hierarchical linear model was used to investigate the relationship between objective and subjective reactivity. Time was the only predictor in the first step, subjective reactivity was added as a predictor in the second step, and the time x subjective reactivity interaction was explored in the final step. Subjective reactivity was not found to moderate the relationship between time and cannabis use, although there was a significant relationship between self-reported subjective reactivity and variability of cannabis use across the data collection period. CONCLUSIONS: This study determined that participants who report greater subjective reactivity to cannabis measurement are more likely to demonstrate variability in their cannabis usage. While this study did not find a significant change in cannabis scores over time because of reactivity, the non-significant results are valuable from both a research and a clinical standpoint. For research, the lack of change is an indicator that reactivity is likely not a confounding factor in studies involving cannabis daily diary research. From a clinical perspective, the non-significant change indicates that simply self-monitoring cannabis is unlikely to provide standalone benefits when daily self-monitoring is used in clinical practice. It is relevant to note that our study involved a non-help-seeking sample, and future research could benefit from determining whether cannabis reactivity may be moderated by help-seeking behaviours or motivations to change.
Examining measurement reactivity in daily diary data on substance use: Results from a randomized experiment
