Since the US recently went on to DST, I thought it'd be appropriate to ask this:
I've heard many claims made about DST, ranging from "It saves electricity" to "It balances out daylight hours" to "It gives people more sunlit free time in the evenings." Which of these claims are true, and what evidence supports those claims?
Edit: I should probably consider both positive and negative effects, and not just benefits. Question title edited to reflect that.
I read a Scientific American article on this a while back. It had this to say about Daylight Savings in the USA:
People may think that with the time shift, they are conserving electricity otherwise spent on lighting. But recent studies have cast doubt on the energy argument—some research has even found that it ultimately leads to greater power use.
The observed drop in energy use of 0.2 percent fell within the statistical margin of error of 1.5 percent.
The article also addresses concerns about an increase in heart attacks, but also lowered traffic accidents. In today's society, I think that the idea persists mostly out of momentum more than sound science.
In 2008 there was a study published that showed DST wastes energy in Indiana. The authors took advantage of the fact that Indiana legislated state-wide DST in 2006, whereas prior to that they had per-county DST or non-DST. They used the individual home meter readings from the utility company to conclude that DST wasted energy overall.
Focusing on residential electricity demand, we conduct the first-ever study that uses micro-data on households to estimate an overall DST effect. The dataset consists of more than 7 million observations on monthly billing data for the vast majority of households in southern Indiana for three years. Our main finding is that—contrary to the policy's intent—DST increases residential electricity demand. Estimates of the overall increase are approximately 1 percent, but we find that the effect is not constant throughout the DST period. DST causes the greatest increase in electricity consumption in the fall, when estimates range between 2 and 4 percent.
Since this question was posted, there have been many more studies in the literature about the effects of DST. Here I just summarize the first 13 papers (some are gated) that show up on Google Scholar ("Daylight Saving Time", with filter 'since 2010')
My tl;dr conclusion: Most but not all say DST is bad.
Energy-related
(1) uses a natural experiment in Indiana:
DST saves on electricity used for illumination but increases electricity used for heating and cooling. ... the latter effect is larger ... DST costs Indiana households an average of $3.29 per year in increased electricity bills, which aggregates to approximately $9 million for the entire state. Finally, the social costs in terms of increased pollution emissions range between $1.7 and $5.5 million per year.
(11) finds that in India (which does not currently have DST) will benefit more by advancing the current Indian Standard Time by half an hour, than by adopting DST.
(12) finds that DST reduces electricity consumption by at least 1.0% in both Norway and Sweden.
Sleep/Health/Accidents/Productivity-related
(2) looks at data from Swedish Heart Intensive Care Admission and finds
an elevated incidence ratio of 1.039 [for Acute Myocardial Infarction] for the first week after the spring clock shift forward.
(3) finds "a dramatic increase in cyberloafing behavior".
(4)'s abstract states very tentatively that
Indirect evidence of an increase in traffic accident rates, and change in health and regulatory behaviours which may be related to sleep disruption suggest that adjustment to daylight saving time is neither immediate nor without consequence.
(5)'s abstract suggests that sleep-adjustment difficulties is severest for those who habitually sleep less than 7.5 hours.
(6) looks at Finnish data and concludes: "It seems that sleep deprivation after DST transition is not harmful enough to impact on occupational accident rates." (10) is by some of the same authors and has a similar conclusion.
(8) finds a "rise in Road Traffic Collision related injury figures up to two weeks following the spring time transition." (9) seems to be just an updated version of (8) with the same conclusion.
(13) finds that DST lowers SAT scores.
Other
(7) states there is an "economically large negative daylight-saving effect in U.S. stock returns".
Sources (Journal publication date in parentheses)
(1) Does Daylight Saving Time Save Energy? Evidence from a Natural Experiment in Indiana (Nov 2011)
(3) Lost sleep and cyberloafing: Evidence from the laboratory and a daylight saving time quasi-experiment. (Sep 2012)
(4) The impact of daylight saving time on sleep and related behaviours (Aug 2013)
(6) Work-related accidents and daylight saving time in Finland (Nov 2010)
(7) EFFECTS OF DAYLIGHT-SAVING TIME CHANGES ON STOCK MARKET RETURNS AND STOCK MARKET VOLATILITY (Feb 2013)
(10) Daylight Saving Time Transitions and Road Traffic Accidents (2010)
(11) Year-round daylight saving time will save more energy in India than corresponding DST or time zones (March 2012)
(12) The impact of daylight saving time on electricity consumption: Evidence from southern Norway and Sweden (June 2011)
(13) Detrimental effects of daylight-saving time on SAT scores (Feb 2011)
