Using the discontinuity approach, the results indicated that in lifetime drinkers, DSM-IV lifetime alcohol dependence criteria can be used to represent a linearly increasing continuum of liability using as validators two important risk factors for alcohol use disorders, family history of alcoholism and early age of drinking onset. In addition, a similar linear relationship was found for alcohol abuse and dependence combined, albeit with firmer support when family history was used as the validator than when early drinking onset was used. These results add to evidence suggesting that alcohol abuse and dependence criteria are intermixed and lie on a single underlying continuum. However, in contrast, no support was found for a model including categories either below the DSM-IV diagnostic threshold for alcohol dependence criteria at the present DSM-IV threshold, or for alcohol dependence and abuse criteria at any of several thresholds.
In contrast to the above results, adding a dichotomous lifetime 4+/5+ binge drinking criterion resulted in a significant departure from fit of the model to the data. These results are inconsistent with IRT findings on current (last 12 months) criteria (Saha et al., 2007
) suggesting that such a binge drinking criterion could be added. Two reasons may explain the discrepancy in findings. One reason is that the IRT methodology examines criteria only in relation to each other, while the discontinuity approach not only examines the criteria in relation to each other, but also directly incorporates information from external validators. The other reason is that the discontinuity results for lifetime binge drinking may differ from IRT findings due to the difference in time frame. For example, our analyses included some lifetime binge drinkers who were abstainers in the last 12 months as part of recovery from alcohol dependence (Dawson et al., 2005
). Such individuals would have been omitted entirely from Saha et al. (2007)
. In either case, the difference in findings across the two methods suggests caution in the addition of binge drinking as a criterion to the AUD criteria, since different methods and timeframes should produce consistent results to provide sufficiently strong support to add a new criterion to the existing criteria set in DSM-V.
The discontinuity approach differs from CFA, LCA and IRT or Rasch model analysis in several fundamental ways. First, the discontinuity approach is based on the number of criteria endorsed and not on the properties of the individual items. Second, the approach directly incorporates validation of the criteria set through study of their relationship to key validators (factors well known to be related to the diagnoses but not included in the criteria set). Third, the approach allows for adjustment for important covariates, a feature not available in latent class or IRT analysis. Fourth, the method addresses observed rather than latent variables. Further, the discontinuity approach has been described as advantageous since it avoids the assumptions required of LCA and IRT that are not always met in practice (Helzer et al., 2007
). Thus, the discontinuity approach offers the advantage of an additional methodology in evaluating alterations to existing sets of diagnostic criteria.
Two genetic association studies provide a useful illustration of the utility of the additional information provided by a dimensional indicator of lifetime DSM-IV alcohol dependence criteria like Model 2 (M7Dimensional
) compared to the binary diagnosis with its arbitrary threshold. Both studies addressed the same allelic variant, and analyses in both studies faced a situation in which statistical power was limited, in one case because the allele of interest was rare (Heath et al., 2001
) and the other case because the allele of interest was not rare but the sample was small (Hasin et al., 2002
). In both studies, the relationship between a binary diagnosis of DSM-IV alcohol dependence and the allele of interest was in the predicted direction but not statistically significant. However, when dependence was used as a dimensional variable (range 0–7), the predicted relationships between the allele and dependence became significant. These results can be seen as an additional external validation of the dimensional approach to alcohol dependence, in this case, using a biological validator, and support the use of a dimensional approach in other situations of interest where power is limited, e.g., in testing gene × gene or gene × environment interactions. To our knowledge, studies of the 11-criterion continuous measure including abuse and dependence in relation to specific genetic variants have not yet been conducted. These would be informative about the validity of this continuous construct of alcohol use disorders. If validated in genetic studies, such a quantitative variable has the potential to improve the power of genetic studies.
The lack of any evidence for a diagnostic threshold if the alcohol abuse and dependence criteria are combined in DSM-V indicates that a decision regarding a diagnostic threshold will be difficult to make. This problem will need to be overcome if the abuse and dependence criteria are combined, since DSM-V will continue to require diagnostic thresholds. The method of resolving this problem (aside from an arbitrary decision) is not obvious. An alternative solution that avoids the need for a new diagnosis and threshold, while addressing the need to note both abuse and dependence criteria, is to retain both disorders but remove the DSM-IV hierarchical structure requiring that abuse not be diagnosed if dependence criteria are met. Such a decision would also address the fact that women and minority groups differ in their likelihood that alcohol dependence is accompanied by abuse (Hasin and Grant, 2004
) and remove confusion about whether to make a dependence diagnosis condition on meeting criteria for abuse (Grant et al., 2007
Some investigators prefer a focus on the current (or last 12 month) timeframe than the lifetime timeframe on the grounds that recent events are more likely to be recalled and reported than more temporally distant events. We agree with these concerns about reporting and recall. However, the diagnostic criteria need to work well in both current and lifetime timeframes, as the latter is the timeframe for most genetics studies, and for many epidemiologic purposes as well. In fact, assessing a history of past disorders is also commonly part of a clinical evaluation. Despite potential difficulties of recall, the seven DSM-IV dependence criteria have been shown to have excellent reliability and validity in both current and lifetime timeframes under a number of paradigms, including the discontinuity approach results shown above. Therefore, all-encompassing concerns about the lifetime timeframe are misplaced in this regard. It is when one moves from the DSM-IV dependence diagnostic criteria to the proposed revisions that incorporate the aggregation of dependence, abuse and binge drinking that problems begin to arise. For this reason, we suggest caution in incorporating these criteria together in a DSM-V alcohol use disorders category.
Our concerns about binge drinking are not specific to binge drinking per se
but would pertain to the proposal of any new criterion. A criterion should have consistent evidence supporting its addition across studies with different designs. We focused on binge drinking because this alcohol-related behavior has already received attention as a proposed new criterion (Saha et al., 2007
; Li et al., 2007
). We used the discontinuity approach to investigate binge drinking due to our results on the relative fit of different models of dependence to the NESARC data when only seven DSM-IV alcohol dependence criteria were examined (above and Hasin et al., 2006a
). We reasoned that the excellent fit of the model to the data for the seven criteria should be maintained with additional criteria if they were valid. Further, if DSM-V severity measures can be based on the diagnostic criteria, then clinicians can assess severity more efficiently than if assessment of different conditions is required (First, 2005, p. 563). We therefore considered binge drinking in that context. Addition of binge drinking as a criterion resulted in a significant departure from a linear model, suggesting caution in adding it to the existing criterion set for alcohol use disorders.
Study limitations are noted. First, consistent with other epidemiologic studies, dependence and abuse symptoms were measured via retrospective structured self-report rather than observation, as was family history and early drinking onset. However, all variables had good to excellent test–retest reliability and the measures of alcohol use disorders have been validated in many paradigms, including psychiatrist reappraisal (Canino et al., 1999
). Also, to reduce misclassification, we created the binge drinking variable from frequency and quantity indicators instead of questions specifically asking about these particular quantities. The focus on observed rather than latent variables could be seen as a limitation, since this method does not attempt to remove measurement error. However, results based on observed variables that appear clear and strong can add to what is known on a specific research question. Other strengths of the work include a focus on lifetime rather than current variables, a timeframe that is important for epi-demiologic and genetic studies, use of a method that does not make some of the assumptions of other methods (Helzer et al., 2007
), and direct incorporation of important and well-established risk factors into evaluation of the different patterns of criteria we examined.
Our study evaluated the dimensionality of lifetime alcohol abuse and dependence criteria to provide information for DSM-V, and for purposes of refining variables for use in genetics and epidemiologic studies. A useful quantitative phenotype should be correlated with diagnosis and also represent severity of a disease (Almasy, 2003
). Using validating variables such as age of drinking onset or family history gives meaningful context because they reflect susceptibility (Almasy, 2003
). An advantage to using such a quantitative measure (as compared to other severity indicators that may not be assessed in a standardized way from study to study) is the potential for reproducibility across studies that have already assessed all DSM-IV alcohol abuse and dependence criteria. Our results suggest potential value in exploring a combined quantitative indicator including dependence and abuse criteria in genetic analyses. Finally, the results contribute information based on a different approach to what is known about the performance of alcohol abuse, dependence and binge drinking as criteria for alcohol use disorders in DSM-V. As the present period is one in which convergent information across multiple studies and methods is actively sought by the DSM-V Substance Use Disorders Workgroup, the results are timely.