Public Release: 

How To Test Whether Workers Are "Fit For Duty"

Human Factors and Ergonomics Society

Excerpts from "Fit for Duty?" by James C. Miller, in ERGONOMICS IN DESIGN, Volume 4, Number 2, April 1996. Copyright 1996 by Human Factors and Ergonomics Society, P.O. Box 1369, Santa Monica, CA 90406-1369 USA; 310/394-1811, fax 310/394-2410, To obtain a copy of the entire article, which includes full references and brief overviews of a number of testing tools on the market, contact Lois Smith at or at the address above.

There is considerable concern over impairment in the workforce and the effect this impairment has on safety and productivity. When one considers only the everyday factors that may restrict job performance, such as fatigue and illness, the overall effect on safety and productivity clearly becomes significant and merits the development of countermeasures.

Urine testing is one such countermeasure for drugs, but the collection and laboratory testing of bodily fluids is a costly and time-consuming procedure. For this reason, urine testing is typically used on a random basis. Additionally, the turnaround time is too slow to provide a true fitness-for-duty screening method. Low-cost devices or procedures are needed that quickly, conveniently, and reliably assess employees' fitness for duty and that are legally and socially acceptable.

This is a companion piece to an article that appeared in the January 1995 issue of ERGONOMICS IN DESIGN (Gilliland & Schlegel, 1995). My focus here is on detecting occurrences of unfitness for work on a daily basis at the worksite, particularly jobs that affect public safety, public health, or other public domain issues. This discussion is intended to provoke reflection and discussion about the issue of daily fitness-for-duty testing in the workplace.

Types of Fitness-for-Duty Testing

One may take a number of approaches to test for fitness for duty in the workplace: performance, neurological, and biochemical measurement. The three approaches are probably complementary: biochemical and neurological measures assess lifestyle, which is appropriate for some occupations, and performance measures assess immediate, job-relevant issues.

Some investigators who have published information about the effects of stressors on performance measures in the performance category have suggested informally that fatigue or environmental stressors may impair the higher cognitive functions first, perception next, and motor functions last. For example, automated or highly overlearned tasks such as tracking may be more resistant to fatigue than mental tasks such as decision making and other higher cognitive tasks involving short-term memory and attention. Electroencephalographic data indicate that one can steer a vehicle successfully on a straight highway while the brain s cortex is asleep (O Hanlon & Kelley, 1977).

Measurements of higher cognitive functions may provide sensitive indices for evaluating fitness for duty. In other words, a relatively large proportion of detections of impairment will occur among those who are truly impaired. Conversely, measurements of motor functions may provide specific indices for evaluating fitness for duty. In other words, a relatively large proportion of nondetections of impairment will occur among those who are truly not impaired. Unfortunately, these two kinds of detections tend to be somewhat reciprocal: One is enhanced at the other s expense. As I will show, the latter may be the higher priority for workplace testing.

Performance Tests

Performance tests may be sorted into several subcategories: motor, perceptual, and higher cognitive. These labels each refer to the highest level of "thinking" (cognition) required to perform a given test. For example, a motor test might simply require that the hand be connected to the eye by normally functioning neural circuits. One reliable motor test measures finger-tapping speed and coordination. A perceptual test might require that one accurately compare patterns, identify colors, or recognize tones as high, medium or low pitch.

Examples of higher cognitive tests include (a) simple mathematical processing, such as adding three-digit sums with reasonable speed and accuracy; (b) code substitution, whereby numbers (digits) are substituted rapidly and accurately for letters (symbols) in a simple code-solving process; or (c) short- term memory tasks in which, for example, a set of letters (say, four) is briefly presented (e.g., one second), followed by a series of letters presented one at a time. The subject's task is to determine if the letters in both sets match.

With most of the commercial tests described in this article, the employee is tested against his or her own baseline using the mixed approach. This procedure avoids some problems associated with the use of population data, including inappropriate discriminations on the bases of age, sex, computer literacy, intelligence, education, dexterity, and even test anxiety. Using the individual as his or her own control also gives one greater sensitivity and specificity than comparisons to a population norm.

Conducting Testing

Daily performance testing seems best suited to the immediate determination of occasions when the employee is not ready to start work. A reliable detection of relevant psychomotor impairment may be made at the start of the work period. However, the manager must remain aware of test limitations associated with the relationship between the nature of the test and the nature of the job.

For example, driving a truck safely requires intact decision- making skills, auditory and visual perception, and eye-hand coordination, among other things. If I test only for eye-hand coordination, I may draw conclusions based only on test failures, not on test passes. When the employee fails the test, he or she discloses that eye-hand coordination, a central nervous system function essential to the job, is not operating well. One may conclude that the employee is likely not to perform safely.

However, when the employee passes the eye-hand coordination test, he or she discloses only that a necessary, but not sufficient, function is working well. I call this exclusion testing. A failure is reason to exclude the employee, at least temporarily, from safety-sensitive work. But other necessary functions have not been tested, so one may not conclude from a test pass that the job will be performed safely. It is difficult to identify-- much less test for--all the cognitive and neuromuscular functions required to perform a job well. Thus, performance testing of the nature discussed here will allow only detections of potentially unsafe situations. Even though it may sharply reduce on-the-job accident probabilities, performance testing cannot guarantee safe job performance.

Worker Acceptance

To date, only scant data have been available that specifically address worker acceptance issues. As Gilliland and Schlegel (1995) noted, workers are more likely to accept a screening test that has good face validity--in other words, if they believe the test relates closely to their job performance capabilities.

During validation tests of the NovaScan (Nova Technology, Inc., or NTI), test participants--employees of a major shipyard in Norfolk, Virginia--were asked their opinions of NovaScan compared with urinalysis. According to Bob O Donnell of NTI, "Sixty-seven percent clearly preferred NovaScan."

My experience with drivers who have been tested daily at their worksite before driving suggests that immediate feedback to management about test results should not be the ultimate objective of fitness-for-duty testing. Professional drivers use their own perceptions of the varying effort they must exert from day to day to pass the test to give themselves feedback about their fitness. Drivers may modify their drinking (alcohol) and sleeping behaviors somewhat to be ready for the test. They may introduce a nap into their schedule. Thus, I suspect that one highly useful application of fitness-for-duty testing will be private, immediate fitness feedback to the professional driver. Most will use it; some will ignore it.

Typically, several aspects of worker acceptance must be addressed. First, each worker experiences the natural fear of the unknown when faced with the prospect of daily testing before driving. With time, the worker realizes that, given adequate rest and an absence of depressant or otherwise psychoactive substances, the test can be passed routinely. The worker therefore progresses from anxiety to comfort and confidence. This dimension is labeled comfort.

One should provide feedback about test performance to workers. This should be no more than a simple, volatile, brief display on the screen at the end of a test (for example, pass or fail). Using this information and many presentations of tests across months of work, workers become able to provide estimates of how well the test results reflect their fitness for duty. Over time, a worker should increasingly perceive a test as an accurate predictor of work performance. This dimension is labeled accuracy.

Management Acceptance

Performance testing introduces some new problems for managers. The employee who is unable to pass a performance test may be impaired because of (a) job-induced fatigue accumulated from work period to work period, (b) non-job-induced fatigue associated with the family (e.g., a new baby in the household) or with outside employment, (c) circadian rhythms in human performance abilities, (d) prescription or over-the-counter medications, or (e) alcohol, illicit substances, and the like. No longer may managers conclude that the impaired employee is guilty of an illegal act, as with urine testing. This being true, what should management do with the employee who fails? What are the patterns of performance test failure associated with acute and chronic employee personal problems?

In Conclusion

The use of performance measurement allows us to assess immediate, job-relevant issues. Now the question before us is, can we use this intelligent technology intelligently?

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