Christopher Barnes and David Wagner, both doctoral candidates studying industrial and organizational psychology, found in two separate studies that the March switch to daylight saving time resulted in 40 minutes less sleep for American workers, a 5.7 percent increase in workplace injuries and nearly 68 percent more work days lost to injuries.
They found no significant increase in workplace accidents or sleep loss, however, when the clocks were set back an hour in November.
The Sleep-Safety Link
But can losing one hour of sleep really make a difference? According to Barnes, it can. "Studies have shown that lost sleep causes attention levels to drop off," he said, and stressed that the impact could be greatest in jobs requiring a high level of attention to detail.
Other existing research supports the researchers' findings. A University of British Columbia study, using data from the Canadian Ministry of Transport, found that when Canada went into daylight saving time, there was an 8 percent increase risk of accidents on the Monday after the changeover. A similar study, using information from the U. S. National Highway Traffic Safety Administration, cited sleep deprivation as the most likely cause of a 17 percent increase in accidents on the Monday following the time change.
Barnes pointed out that is not uncommon for people to complain how tired they are when they lose sleep. Many people adjust to a pace where events recur regularly and they can be adversely affected when that schedule is disrupted. An obvious example is jet lag, which occurs when people travel across several time zones.
"Their internal clocks need some recovery time for these kind of disruptions," Wagner said.
Barnes added that people assume the change to daylight saving time is not going to greatly affect them. After all, it's only one hour. And if they do have an accident or make a mistake, they are not likely to attribute it to sleep loss.
While their study focused on physical accidents, Barnes and Wagner said a logical extension could include mistakes in the office or workplace, such as transposing figures on a spreadsheet or filling the wrong prescription in a pharmacy.
Other Factors
Barnes and Wagner used figures from the American Time Use Survey conducted by the Bureau of Labor Statistics, which included more than 14,000 interviews. They also studied data from MSHA. In analyzing those figures, it was clear that people lost an average of 40 minutes of sleep following the change to daylight saving time and there was a jump in workplace accidents following the time change.
They examined all Mondays in a year and allowed for seasonal effects and other factors. For example, there is more likelihood of snow in Michigan and Minnesota in March than in other parts of the country, and the bad weather may have been more of a contributing factor to accidents than the time change.
However, the results clearly show that sleep does have a profound effect upon human behavior and lack of sleep can have significant and serious results, they said.
So, when next March rolls around and clocks are turned forward an hour, organizations should be aware that daylight saving time may save daylight, but not without some cost to organizations.
The research will be reported in the September issue of the Journal of Applied Psychology.