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Wednesday, August 05, 2009


The decisive criteria is PPV. According to PPV, each screen is very weak.

As we mentioned in the WAGER 14(6), positive predictive value (PPV) is one of several psychometric properties, and the purpose for the screening, not the different properties, determines the best fit. Concerning your assertion that the PPV is ‘weak’ for both screens, screens that target low base rate disorders tend to have low PPV’s. The PPV’s for the NODS-CliP and BBGS (i.e., 0.13 and 0.37 for respectively) compare quite favorably with brief screens that target other low base rate phenomena. Donker, van Straten, Marks and Cuijpers (2009) found PPV’s similar to the BBGS for screen of numerous mental health and substance abuse disorders that typically have higher prevalence rates (Kessler, Berglund, Demler, Jin, & Walters, 2005) compared to pathological gambling (e.g., obsessive compulsive disorder, lifetime prevalence=1.6%, PPV=0.15; panic disorder, lifetime prevalence=4.7%, PPV=0.10; generalized anxiety disorder, lifetime prevalence=5.7%, PPV=0.29; post-traumatic stress disorder, lifetime prevalence=6.8%, PPV=0.11; alcohol abuse/dependence, lifetime prevalence=18.6%, PPV=0.34). With a PPV of 0.37, the BBGS represents a meaningful advance in a nascent area of public health.

Donker, T., van Straten, A., Marks, I., & Cuijpers, P. (2009). A brief web-based screening questionnaire for common mental disorders: Development and validation. Journal of Medical Internet Research, 11(3).
Kessler, R. C., Berglund, P., Demler, O., Jin, R., & Walters, E. E. (2005). Lifetime Prevalence and Age-of-Onset Distributions of DSM-IV Disorders in the National Comorbidity Survey Replication. Archives of General Psychiatry, 62(6), 593-602.

The WAGER’s comparison of the NODS-CLiP with the BBGS, a screen developed by two of its staff members and a colleague, fails to consider the following highly critical issue:

The clinical validity and diagnostic reliability of the NODS, from which the NODS-CLiP is derived and against which it was benchmarked, were established by its authors (of which I am one) prior to fielding the NODS, and these psychometrics have subsequently been confirmed by other researchers on several continents, as cited in the paper by Toce-Gerstein and her colleagues (in press).

In contrast, zero studies have been published on the clinical validity or diagnostic reliability of the AUDASIS-IV gambling module (AGM), from which the BBGS is derived and against which it is benchmarked. The citation authored by Grant, Dawson, and colleagues (2003), which is the cited basis for evaluating the psychometric properties of this benchmark, clearly reports that no clinical validity studies of the AGM were undertaken prior to its deployment in the NESARC, and as to its diagnostic reliability—as opposed to the test-retest reliability of individual items in non-clinical cases—that could not even be estimated because zero cases of pathological gambling (that is, a score of five or more DSM symptoms) showed up in the test-retest sample that Grant and her colleagues report on.

I have other issues with The WAGER’s comparison, but this one huge hole under the BBGS is sufficient to sideline it from entering any purported contest of virtues.

The WAGER paper ignores one very important matter.

The NODS-CLiP is based on and checked against the NODS. The inventors of the NODS tested its clinical validity and reliability before they used it, and their good test results have been confirmed repeatedly by others, as noted in the cited paper by the Toce-Gerstein team.

The BBGS is taken from and checked against the gambling items in the AUDASIS-IV. Grant and her team are the only ones who have tested these items. Their report clearly says that no study of the validity of these items has been done, and they could not estimate clinical reliability because no cases of pathological gambling showed up in their test/retest study.

There are other problems with THE WAGER paper, but this one huge hole under the BBGS is enough to keep it even from entering the field of “battle.” The NODS-CLiP “wins” by default.

One would expect to see differences in psychometrics between the two screens, as the NODS-CLiP measures lifetime, while the BBGS measures last 12 months. There is increasing evidence that the majority of people who develop gambling related problems move in and out of problem gambling episodes and like most "addictions" the majority of people cease the problematic behaviour of their own accord. Sets of lifetime questions will always be more likely to generate false positives because of the more often transient nature of problem gambling. It makes sense to have a single questions relating to lifetime, but not every question in a screen.

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