Cannabis: Summary of research methodology
“Persistent cannabis dependence and alcohol dependence represent risks for midlife economic and social problems: A longitudinal cohort study,” Magdalena Cerda, et al. Clinical Psychological Science, online, day/date TBD.
- For the current cannabis study, the authors assessed the frequency and duration of cannabis use among participants in the long-term Dunedin Multidisciplinary Health and Development Study — a four-decade project maintained by the University of Otago that has been following the development of a group of 1,037 children born in 1972-1973 in Dunedin, New Zealand from birth to age 38. The Dunedin study includes participants who represent the full range of socioeconomic status and health in the general population and have had follow-up examinations at ages 3, 5, 9, 11, 13, 15, 18, 21, 26, 32 and, most recently, at 38.
- 947 of the 1,037 participants who had completed at least three of the five adult cannabis assessments from ages 18 through 38 were included in the current study. The authors measured both persistence of cannabis dependence, as defined by the total number of study periods out of five that the participant met criteria for cannabis dependence, and persistence of regular cannabis use as the total number of study periods out of five that a participant used cannabis for four or more days per week.
- The cannabis-dependence groups ranged from those who never used cannabis; those who used it at least once but were not diagnosed; and those who were diagnosed as cannabis dependent at one, two, or three or more follow-up assessment periods. The regular cannabis use groups ranged from those who never used cannabis; those who used but never regularly; and those who used regularly at one, two, or three or more follow-up assessments.
- Eighteen percent, or 173 participants, were considered marijuana dependent in at least one wave of the study, and 15 percent (140 participants) fell into the regular cannabis use categories, in at least one wave of the study. Results were similar for persistent cannabis dependence and persistent regular cannabis use.
- Cannabis dependence is a substance use disorder as defined by the Diagnostic and Statistical Manual (DSM) of the American Psychiatric Association. The purpose of the DSM diagnosis is to predict a patient’s future prognosis, and to identify which patients are most in need of scarce treatment resources. A diagnosis of cannabis dependence is given to someone who keeps using despite significant health, social or legal problems.
- The authors measured economic and social problems at age 38 using both self-reported questionnaires and public data, such as credit ratings, court records and government social-welfare benefit records. Socioeconomic mobility was measured by comparing social class in childhood (highest occupational status of either parent from the participant’s birth to age 15) with social class in adulthood (most recent occupation of the participant at age 38).
- Measures of financial difficulties included self-reported net worth, troubles with debt and cash flow, difficulty to pay basic expenses and food insecurity, as well as New Zealand government records of welfare benefit receipt and credit ratings. Measures of relationship conflict included self-reported relationship quality, intimate-partner physical abuse and intimate-partner controlling abuse. Antisocial workplace behavior measures included self-reports of interpersonal deviance, productivity deviance and property deviance. New Zealand government records were used to determine whether participants were convicted of traffic offenses between ages 32-38 years.