The role of cannabis use within a dimensional approach to cannabis use disorders

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Abstract

Context

Cannabis consumption is central to diagnosis of cannabis use disorders; yet, most research on cannabis disorders has focused just on diagnosis or criteria. The present study examines the ability of a frequency and quantity measure of cannabis use as well as cannabis abuse and dependence criteria to discriminate between individuals across the cannabis use disorder continuum.

Method

A representative sample of USA adults in 2001–2002 (N = 43,093) were queried about the past year frequency of cannabis use and each Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM-IV) cannabis abuse and dependence criterion. Factor analysis and item response theory (IRT) models were used to define the relationship between observed responses and the underlying unobserved latent trait (cannabis use disorder severity) among past year cannabis users (n = 1603).

Results

Factor analyses demonstrated a good fit for a one-factor model both with and without the cannabis use criterion and no differential criterion functioning was demonstrated across sex. The IRT model including the cannabis use criterion had discriminatory power comparable to the model without the cannabis use criterion and exceeded the informational value of the model without the cannabis use criterion in mild and moderate ranges of the severity continuum.

Discussion

Factor and IRT analyses disprove the validity of the DSM-IV abuse and dependence distinction: A single dimension represented the criteria rather than the two implied by the separate abuse/dependence categories. IRT models identified some dependence criteria to be among the mildest and some abuse criteria to be among the most severe—results inconsistent with the interpretation of DSM-IV cannabis abuse as a milder disorder or prodrome of cannabis dependence. The consumption criterion defined the mild end of the cannabis use disorder continuum and its excellent psychometric properties supported its consideration for inclusion in the next edition of DSM as a criterion for cannabis use disorders. Additional work is needed to identify candidate consumption criteria across all drugs that apply to the milder end of the severity continuum while also improving overall model performance and clinical diagnostic utility.

Introduction

In the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM-IV; American Psychiatric Association, 1994), cannabis abuse and dependence are defined as maladaptive patterns of cannabis use leading to clinically significant impairment or distress, as manifested by at least one of four abuse symptoms criteria or three of six dependence symptom criteria, respectively. As noted by Saha et al. (2007), despite the central role of consumption in the DSM-IV classification of cannabis disorders, no specific pattern of cannabis use is defined nor do maladaptive patterns of cannabis use appear as diagnostic criteria for either disorder in the DSM-IV. For the most part, research on cannabis use disorders has ignored the actual use of the substance.

A further issue related to the DSM-IV classification of cannabis use disorders is whether abuse and dependence criteria are categorical conditions or may be better represented by a dimensional approach. Are abuse and dependence unique, distinct disorders? Or do the phenomenological presentations better fit continuous measures (i.e., dimensions)? This issue parallels recent calls to add a dimensional component to all psychiatric diagnoses (Krueger et al., 2004, Krueger et al., 2005), and recently, researchers have answered this call by using item response theory (IRT). Published findings using IRT analyses have found strong evidence supporting a single latent dimension underlying DSM-IV alcohol abuse and dependence criteria and items (Krueger et al., 2004, Langenbucher et al., 2004, Proudfoot et al., 2006, Kahler and Strong, 2006, Saha et al., 2006, Saha et al., 2007), and the less extensive IRT literature for DSM-IV cannabis use disorders (Teeson et al., 2002, Langenbucher et al., 2004, Lynskey and Agrawal, 2007, Martin et al., 2006, Gillespie et al., 2007) similarly found better fits for a model specifying a unidimensional latent trait of cannabis use disorder severity. These studies also identified few diagnostic criteria that discriminated at the milder levels of the cannabis use disorder severity continuum, highlighting the need for measures that discriminate across the entire spectrum of severity, especially components that represent milder cases.

One limitation of IRT analyses conducted to date on cannabis use disorders is the unrepresentativeness of the research samples. The two exceptions to this rule are the study by Teeson et al. (2002) and the study by Lynskey and Agrawal (2007) using general population samples of adults age 18 and older. In another study, the sample consisted of adult male twins selected from the Virginia Twin Registry (Gillespie et al., 2007). The remaining two samples consisted of adolescent (Martin et al., 2006) and adult (Langenbucher et al., 2004) substance abuse inpatients and outpatients. The second limitation of these studies was the selection of the target sample of cannabis users to form the basis of the IRT analyses. In these studies, analyses were conducted among cannabis users narrowly defined as those individuals who reported using cannabis at least five times in the previous year (Teeson et al., 2002), at least once a month for six months (Martin et al., 2006) or who reported using cannabis at lest five times during their lifetime (Langenbucher et al., 2004). In the other IRT study (Gillespie et al., 2007), individuals who endorsed using a drug six or more times in their lifetime but not 11 times in one month may have only been asked symptom items related to cannabis abuse, whereas those endorsing use 11 times in one month were asked all cannabis abuse and dependence criteria symptom items. As a result of these limitations, variability in cannabis use was restricted in all studies, and the use of consumption as a screen for cannabis dependence in one study (Gillespie et al., 2007) may have omitted numerous individual with dependence from the analysis. Third, except for the study by Teeson et al. (2002), previous studies conducted their psychometric analyses among lifetime cannabis users and examined lifetime endorsements of cannabis abuse and dependence criteria; measures which are particularly subject to recall bias.

To determine whether cannabis abuse and dependence measure a unitary dimension of cannabis use disorder, large representative samples of the general population are needed that do not restrict variability in cannabis use or dependence and that use current measures of cannabis use and disorder criteria to reduce substantially the risk of recall bias. Accordingly, the purpose of the present study was to determine whether the DSM-IV abuse and dependence criteria defined a cannabis use disorder continuum using a large (n = 43,093) nationally representative sample of the U.S. population, the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). IRT methodology was used: (1) to examine the ability of each 12-month DSM-IV cannabis abuse and dependence criterion to discriminate between individuals across the cannabis use disorder continuum among respondents who had used cannabis during the year preceding the interview; and (2) to determine the differential severity of DSM-IV cannabis abuse and dependence criteria.

To our knowledge, no previous study has examined the role of cannabis use as a candidate criterion for cannabis use disorders, though pioneering research in this area has been conducted for alcohol consumption criteria (Li et al., 2007, Saha et al., 2007). In view of the important role played by cannabis use in DSM-IV definitions of cannabis abuse and dependence, and previous findings of the absence of criteria to represent the mild end of the cannabis use disorder continuum, a cannabis use quantity-frequency measure (i.e., consuming at least one joint per week in the year preceding the interview) was also examined to determine if it could serve as a potential candidate criterion to represent the milder end of the cannabis use disorder continuum. Identification of milder criteria is critical to etiologic research on cannabis use disorders through the development of dimensional measures that discriminate across the spectrum of severity. Accordingly, IRT models with and without the consumption criterion were compared with respect to model fit and information value. In addition, the relatively large sample size of the NESARC allowed for the examination of differential criterion function (DCF) versus invariance of the criteria across sex, an analysis infrequently conducted in past research due to small sample sizes.

Section snippets

Sample

The 2001–2002 NESARC is a study of a representative sample of the USA conducted by the National Institute on Alcohol Abuse and Alcoholism (NIAAA), described in detail elsewhere (Grant et al., 2003, Grant et al., 2004). The NESARC target population was the civilian non-institutionalized population residing in households and group quarters, 18 years and older. Face-to-face interviews were conducted with 43,093 respondents, with a response rate of 81%. Blacks, Hispanics and young adults (ages

Prevalence and factor analyses

The one-year prevalences of DSM-IV abuse and dependence criteria ranged from 2.4% for legal problems to 27.9% for hazardous use (Table 1). The rate of consuming at least one joint a week during the year preceding the NESARC interview was 45.0% among current cannabis users.

Consistent with the recommendations of Hu and Bentler (1999), the one-factor solution demonstrated a very good fit to the observed data underlying the DSM-IV cannabis abuse and dependence criteria both with and without the

Discussion

Both factor and IRT analyses indicated the utility of conceptualizing DSM-IV cannabis abuse and dependence criteria along a dimensional scale of severity. Regardless of whether the cannabis use criterion was entered into the model, factor analyses results indicated that a one-factor model provided a good fit to the data. IRT results showed that the diagnostic criteria for cannabis abuse and dependence (with or without the cannabis use criterion) can be effectively modeled along a unidimensional

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