<P> DST also hurts prime - time television broadcast ratings, drive - ins and other theaters . </P> <P> Changing clocks and DST rules has a direct economic cost, entailing extra work to support remote meetings, computer applications and the like . For example, a 2007 North American rule change cost an estimated $500 million to $1 billion, and Utah State University economist William F. Shughart II has estimated the lost opportunity cost at around US $1.7 billion . Although it has been argued that clock shifts correlate with decreased economic efficiency, and that in 2000 the daylight - saving effect implied an estimated one - day loss of $31 billion on U.S. stock exchanges, the estimated numbers depend on the methodology . The results have been disputed, and the original authors have refuted the points raised by disputers . </P> <P> In 1975 the U.S. DOT conservatively identified a 0.7% reduction in traffic fatalities during DST, and estimated the real reduction at 1.5% to 2%, but the 1976 NBS review of the DOT study found no differences in traffic fatalities . In 1995 the Insurance Institute for Highway Safety estimated a reduction of 1.2%, including a 5% reduction in crashes fatal to pedestrians . Others have found similar reductions . Single / Double Summer Time (SDST), a variant where clocks are one hour ahead of the sun in winter and two in summer, has been projected to reduce traffic fatalities by 3% to 4% in the UK, compared to ordinary DST . However, accidents do increase by as much as 11% during the two weeks that follow the end of British Summer Time . It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring clock shifts . A correlation between clock shifts and traffic accidents has been observed in North America and the UK but not in Finland or Sweden . If this effect exists, it is far smaller than the overall reduction in traffic fatalities . A 2009 U.S. study found that on Mondays after the switch to DST, workers sleep an average of 40 minutes less, and are injured at work more often and more severely . </P> <P> DST likely reduces some kinds of crime, such as robbery and sexual assault, as fewer potential victims are outdoors after dusk . Artificial outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime . </P>

When did daylight saving time start and why