Applying quality control charts to the analysis of single-subject data sequences.

Techniques from the field of quality control can be used to classify the quality of individual samples of physical or cognitive performance. After stable baselines have been established for an individual, deviations in performance can be evaluated using control charts. The effectiveness of this approach in evaluating cognitive performance was tested using databases collected under a variety of risk factors. The sensitivity and specificity characteristics of Shewhart, cumulative-sum (CUSUM), and exponentially weighted moving average (EWMA) control charts were determined for a total of 174 trials involving 10 participants and 23 cognitive performance assessment measures. The most effective technique in each case was typically a function of the specific performance measure and the type of performance change being evaluated. Sensitivity and specificity for the best techniques were as high as 100%. This study demonstrated the usefulness of quality control charts as a tool to evaluate individual participant perform ance over time. Actual or potential applications of this research include readiness-to-perform screening of industrial workers in order to improve the health and safety of the workforce. INTRODUCTION Background The term risk refers to the potential for danger, loss, or injury. A factor is any condition that leads to a specific result. Taken collectively, a risk factor is any condition commonly considered to have the potential for negatively affecting or causing danger to an individual or within the individual's realm of responsibility. A multitude of risk factors exist that can be detrimental to human performance, and their effects on human performance have been studied extensively using descriptive and empirical research in both laboratory and applied environments. Risk factors such as alcohol (Gawron & Ranney, 1988; Maylor & Rabbitt, 1987), over-the-counter and illicit drugs (Hurst, 1976; Starmer, 1985), fatigue and sleep loss (Mertens & Collins, 1986; Steyvers, 1987), and various hostile environments have at some level been linked to either cognitive or physical performance decrements. Exposure to these risk factors may occur off the job or result from hazards imposed by the nature of the job itself. It is common to think of alcohol and drug use when referring to such risk factors. However, fatigue, mental stress, illness, and even microgravity may present serious hazards to the employee and others affected by the employee's job performance. To minimize problems associated with on-the-job impairment, many employers have implemented screening programs designed to assess an employee's readiness to perform (RTP) at the workplace. Gilliland and Schlegel (1993) defined readiness to perform as "that state in which a person is prepared for a job, is capable of performing it, and is free of any transient risk factors that might influence performance" (p. 3). RTP testing is undertaken with the goals of identifying changes in an individual's performance that may have been driven by exposure to risk factors and determining the specific aspects of performance that are immediately affected. Traditional methods of assessing readiness to perform focus on biochemical drug screening (Miller, 1994). Controversy surrounds drug screening, however, including issues concerning privacy, expense, data processing time, and specificity of results. An alternative method of assessing readiness to perform involves neurological evaluation. Although many of these tests are easy to administer and the results are immediately available (e.g., balance control and control of visual gaze), some of the more objective tests (e.g., electroencephalographic and pupillary responses) require extensive testing apparatus and training of the test administrator. Although biochemical and neurological techniques are often successful in detecting the use of chemical substances, they ignore other factors, such as fatigue and stress, that could potentially impair performance. …