The results of this study indicate that the positive predictive value of suspected alcohol and drug violations in aviation employees is rather low; the majority of the employees suspected of using alcohol or drugs tested negative for these substances. The limited accuracy of suspected alcohol and drug violations is due in part to the very low prevalence of alcohol and drug violations in aviation employees. It also reflects the difficulty of identifying alcohol and drug violations through observation of employees’ physical and behavioral characteristics by trained personnel. The exceptionally low PPV of suspected drug violations suggests that it is harder to detect a person under the influence of illicit drugs than a person under the influence of alcohol based on physical appearance, body odor, behavior, and job performance.
On the other hand, the very high positive likelihood ratios indicate that, on a relative scale, reasonable-cause testing is a method with formidable discriminative power for distinguishing employees who are under the influence of alcohol and drugs from those who are not. The discriminative power of reasonable-cause testing suggests that, despite its limited positive predictive value, physical and behavioral observation represents an efficient screening method for detecting alcohol and drug violations. Based on data presented in this study, under the reasonable-cause testing program it takes an average of 3 tests for detecting one alcohol violation and 8 tests for detecting one drug violation.
Both random testing and reasonable-cause testing aim to reduce alcohol and drug violations and may have a deterrent effect. The deterrent effect of random testing is presumably a function of the testing rate. Although little is known about the relationship between the testing rate and the effect size of deterrence, it is reasonable to assume that the deterrent effect increases as the testing rate increases, and vice versa (3
). Results of the present study provide empirical evidence that the deterrent effect of random alcohol testing may diminish as the testing rate decreases. Part of the observed increase in the prevalence of alcohol violations during 1998–2005 might be due to the decrease in annual testing rates from 25% to 10%. The relationship between testing rate and deterrent effect appears to be substance-specific and may be susceptible to extraneous confounders, as evidenced by the lack of any statistically significant change in the prevalence of drug violations after the annual testing rate for drugs was lowered from 50% to 25% in 1998.
Kraus and Li [25
] documented the importance of reasonable-cause testing in detecting alcohol violations among flight crew members. During 1990 and 2006, newspapers reported on a total of 13 incidents of alcohol-impaired flying involving 17 US airline pilots; of the 13 reported incidents, nine were identified by airport personnel and two by passengers based on suspicion of alcohol use by the pilot [25
]. Widespread publicity generated by these incidents may have served as an important mechanism of the deterrent effect of the reasonable-cause testing program.
Although it is not as efficient as reasonable-cause testing in detecting alcohol and drug violations, random testing as an indiscriminate program may be more acceptable to employees than reasonable-cause testing. Moreover, random testing provides essential data for determining the prevalence and monitoring the time trends of alcohol and drug violations, and for evaluating the effectiveness of intervention programs. Therefore, it is important to keep random testing in the mandatory alcohol and drug testing program. The challenge facing researchers and policy-makers is to optimize the different components of the testing program so that the testing program is most cost-effective and cost-beneficial. To meet this challenge, research is needed to quantitatively define the relationship between the annual testing rate for random testing and the deterrent effect on alcohol and drug use behaviors and to understand the extent to which they meet their respective objectives.
This study has several limitations. First, our analysis relied on aggregated alcohol and drug testing data. Employee-level data were not available. Therefore, it was not possible to examine alcohol and drug violations by demographic characteristics. Second, the validity of suspected alcohol and drug violations was measured only by positive predictive value and positive likelihood ratio. We did not have data necessary for estimating the sensitivity and specificity of reasonable-cause testing. The negative predictive values of reasonable-cause testing are likely to be higher than 99%, given the very low prevalence (<1%) of alcohol and drug violations in aviation employees. Third, we did not examine the intra- and inter-observer reliability of suspicions of alcohol and drug violations. The reproducibility of physical and behavioral observations is likely to vary with many factors, such as timing, individual response to alcohol and drugs, and observer’s experience. To enhance the performance of reasonable-cause testing requires improving both the validity and reliability of the observational method for detecting physical and behavioral characteristics related to alcohol and drug use.
The mandatory alcohol and drug testing policy for employees with safety-sensitive functions has been challenged on a number of occasions regarding its constitutionality, admissibility and reliability of the test results, and conflict with the National Labor Relations Act (26
). The mandatory testing programs were opposed by employers on the basis of unnecessary costs to their businesses and by unions on the grounds of unreasonable search in violation of the Fourth Amendment (26
). The alcohol and drug testing policy has been upheld by the courts of law because it is implemented according to uniform and standardized procedural protocols and because it is supplemented by other components of the Federal Drug-Free Workplace Program, such as the employee assistance program that provides confidential counseling and referral to rehabilitation services. Findings from this study and other studies (3
) indicate that the mandatory testing programs hold sufficient safeguards against alcohol and drug abuse by aviation personnel.