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1988) yield information which is different in inconsistent ways from that given by criterion measures or collateral report. Biochemical markers of alcohol consumption have been found to add little to self-report in alcohol patients as they lack sensitivity (Cushman et al. 1984) or specificity (Monteiro and Masur 1986); Limin et al. (1999) additionally found that sensitivity and specificity for both gamma-glutamyl-transferase (GGT) and carbohydrate-deficient transferrin (CDT) were considerably lower in their study than previous reports. In an investigation of the relative utility of these biological markers of alcohol consumption, Mitchell et al. (1997) found that sensitivity was greater for CDT than for GGT while specificity was greater for GGT than for CDT. Drummond and Ghodse (1999) have recommended combining biochemical tests with interview methods to enhance precision in both clinical and research settings.
Problems with concurrent urinalysis in drug users include difficulties in interpretation when the presence of some drugs is suggested by the presence of their metabolite only, the different time lags between use and appearance and disappearance of the drug from the urine, the need to repeat tests and the different ability of tests to detect different drugs. In the case of their use for the purpose of validation of self or collateral report, it has been pointed out by Maisto et al.(1990) that pharmacy preparations may contain compounds of which the user is unaware.
In a recent study, Babor et al. (2000) examined the correspondence between self-reported drinking, biological markers (liver function tests) and reports of collateral informants in a large scale clinical trial of treatment for alcohol problems (Project MATCH Research Group 1997) and concluded that self-report provided the most accurate source of data showing only moderate correlations with collateral report and even lower correlations with biological measures. These authors demonstrated that correlations varied with the timing (pre- or post-treatment) of the data collection and that the feasibility of collecting the different data varied at each data collection point. Therefore these measures could not be used as substitutes for each other, nor could it be concluded that each measure provided information on a unique aspect of drinking because of the possibility that the collateral and biological measures were simply less sensitive to drinking. Their concluding recommendations were to enhance the accuracy of self-report by providing recall cues and emphasising the importance of accurate information.
Midanik reviews other methods which include computer based questionnaires and interviewing, personal interviewing in a variety of techniques and laboratory tests of breath, sweat, urine and blood (hair testing for drugs has been developed subsequently). Given that the laboratory tests, though useful for specific diagnostic and confirmatory purposes can give information with only low specificity and low sensitivity on quantity and frequency of use, Midanik concludes that
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