A study cited in Industrial Health in 2005 found insomniacs in the United States have an average monthly sick absence rate that is 1.4 times greater than people without sleep troubles. And figures from the US National Commission on Sleep Disorders suggest insomnia in the workplace costs the US economy between $92 and $107.5 billion a year in absenteeism and workplace disability, lost productivity, mistakes, and accidents. In the United Kingdom that figure was put at £10-12 billion ($18-21 billion) a year.

The dollar figures explain the ergonomic and economic impact of insomnia, and why there are hundreds of research papers exploring all the aspects of the impairment associated with it.

The latest is a British study, published in May by Oxford University and reported in the British Psychological Society Research Digest. It was built on the doctoral dissertation of Christina Neitzert Semler, which aimed to investigate the effect of monitoring on the discrepancy between real versus perceived daytime impairment in insomnia. For the new study Dr. Semler and Dr. Allison G. Harvey, experimental psychologists at Oxford, tested 21 students who had experienced at least three nights of sleep disturbance per week for the previous month for their study. Using sensitive instruments that monitor movement, the students' sleep was measured for three nights. Each morning an electronic display that the students thought was connected to the monitor told them how well they had slept. Controlled by the researchers, the monitor gave false results and tricked the subjects into thinking they'd had enough or too little sleep. In other words, the results bore no resemblance to the amount of sleep detected by the monitors.

The researchers found that the students in the study group who believed they had slept poorly functioned poorly in the daytime, regardless of the how much or how little they had slept. Though the quality of their sleep didn’t vary significantly from night to night, the "poor sleepers" reported negative thoughts, sleepiness, aching muscles, and sore eyes, and compensated with a daytime nap.

The results led the researchers to conclude that anxiety about not sleeping well causes or worsens the daytime impairment so often reported by insomniacs.

Sources: American Insomnia Association; Industrial Health 2005:43; US National Commission on Sleep Disorders, British Psychological Society Research Digest;"Monitoring for Sleep-Related Threat: A Pilot Study of the Sleep Associated Monitoring Index (SAMI)," published by Oxford University.