Every year I approach the end of March and October with the same growing trepidation, knowing that my sleep pattern is about to be disrupted, and I am going to be tired, grumpy and generally miserable for the best part of a week. Shifting the clocks back and forward an hour to save energy may have made sense in the early nineteen hundreds, but we now know that very little energy is in fact being saved (Havranek T. et al, 2018). In addition to making me fairly unpleasant to be around, the daylight saving time (DST) clock changes have been shown to affect both our physical and mental health.
The most prominent study examining DST-related mental health effects found that the Autumn clock change (when we gain an hour’s sleep) was associated with an 11% increase in hospital visits for depression across Denmark (Hansen BT. et al, 2017). There is also some limited evidence that the Spring transition (when we lose an hour’s sleep) is linked to an increase in suicide death rates (Lindenberger LM. et al, 2019). However, evidence of the more general effects of the transitions on mental wellbeing is sparse. To date, two studies have focused on self-reported life satisfaction, with both reporting a small reduction in life satisfaction after the Spring clock change (Kuehnle D. & Wunder C., 2014; Kountouris Y. & Remoundou K., 2014).
In a new study, Costa-Font and colleagues (2024) aimed to extend the work of these studies by:
- Comparing differences in life satisfaction over the clock changes to differences around the last Sunday of the month in adjacent months (as a counterfactual).
- Examining a wider range of outcomes to explore the possible mechanisms underlying the reported mental health effects.
- Performing a cost-benefit analysis of abolishing the DST clock changes.
Research suggests that the Spring daylight saving time clock change is linked to a small reduction in life satisfaction.
Methods
The authors analysed data from the German Socio-Economic Panel (SOEP) between 1984 and 2018. The study sample consisted of adults interviewed in the two weeks either side of the Spring and Autumn clock changes. They also interviewed participants in the two weeks either side of the last Sunday of the month in the two previous and two subsequent months (as the counterfactual). Participants were asked to rate how satisfied they were with their life and their sleep (0 = completely dissatisfied; 10 = completely satisfied). They were also asked how often, in the last four weeks, they had felt pressed for time or their mental health had affected their work/everyday activities.
The researchers used several approaches to address their research question:
- A design called regression discontinuity (RD) was applied to compare responses just before and after the Spring and Autumn clock changes.
- An RD design was used along with a differences-in-differences (RD-DiD) design to compare the RD results to the average difference in responses seen in the counterfactual months.
- Heterogeneity (diversity) in effects were explored by splitting analyses by sociodemographic subgroups, such as male/female, employed full-time/part-time, with/without children, blue/white collar worker, hours worked and low/high time stress.
- Event study analyses were used to explore longer-term effects by comparing the differences in responses in the two weeks either side of the clock changes to the two weeks either side of the last Sunday of the month in the counterfactual months.
- Cost-benefit analysis of stopping the DST clock changes was conducted.
Participants were interviewed in the two weeks before and after the clock changes and asked to rate how satisfied they were with their life and their sleep.
Results
Both the RD and RD-DiD analyses showed a decrease in life satisfaction immediately after the Spring transition. The RD analysis found that life satisfaction dropped by 1.39% (-0.058 standard deviations (SD)) after the clock change, whilst the RDD-DiD analysis showed a 1.44% (-0.060 SD) decrease in life satisfaction compared to normal months. This negative effect on life satisfaction persisted for around six days.
In exploring the potential mechanisms through which the clock change may affect life satisfaction, the authors found that sleep satisfaction was reduced (by -0.213 standard deviations (SD)) and time pressure (feeling rushed for time) was raised (by 0.194 SD) after the Spring clock change. Analyses split by sociodemographic subgroups showed that the negative effect of the clock change on life satisfaction only occurred in those who identified as male (-0.213 SD), not in females. A decline in life satisfaction was also experienced amongst people working full-time (-0.084 SD), in blue-collar jobs (-0.358 SD) and with high levels of time stress (-0.083 SD).
In contrast to the Spring clock change, the researchers found that after the Autumn transition life satisfaction increased by approximately 0.114 SD. This means that the Autumn clock change is associated with a 0.114 unit increase on the above-describe life satisfaction questionnaire (a 0-10 scale).
In their cost-benefit analysis the authors estimated that ending the clock changes (taking into account life satisfaction, health and productivity costs) would result in a €754 per capita gain.
Life satisfaction declined after the Spring clock change as a result of a reduction in sleep quality and increased time pressure. The societal cost of this decline is estimated to be €754 per capita gain.
Conclusions
This analysis of German Socio-Economic Panel data concluded that the Spring DST clock change was associated with a small decrease in life satisfaction, largely as a result of sleep loss and increased time pressure. This effect lasted for around 6 days and was mainly seen in men, full-time workers, those in blue-collar jobs and those experiencing high levels of time stress. Abolishing DST in Germany would result in a €754 per capita net gain. The authors argue that wellbeing should be taken into account when DST policies are evaluated.
Men, full-time workers and blue-collar workers experienced a decrease in life satisfaction.
Strengths and limitations
This study examines the wider effects of the DST clock changes on general mental health, not just the most serious effects captured in people’s medical records. A key strength is that it used data over a 34-year period which meant it had a large sample size (>370,000 observations for life satisfaction), making its results more precise and enabling sub analyses to identify those most affected by the clock changes. In addition, in this regression discontinuity design, participants were randomly assigned to being interviewed before or after the clock change, based on the time of the clock change. This means that the two groups should have similar characteristics. It is therefore possible that the clock changes caused the differences found in life satisfaction observed between the two groups (Moscoe E. et al, 2015).
Finally, the study achieved its aim to extend the current literature by conducting a cost-benefit analysis, exploring the mechanisms through which the transitions effect mental health and by including a counterfactual to demonstrate that the differences in life satisfaction seen over the clock changes differ from those seen in other months.
That said, this study does have several limitations that we must consider.
- Firstly, the data analysed was self-reported by participants themselves and therefore may be subject to recall bias as a result of participants forgetting or lying. This can be a particular problem when researching sensitive issues such as mental health where there may be a stigma attached to reporting low life satisfaction or poor sleep.
- Secondly, although the German Socio-Economic Panel data is broadly representative of the German population, if participation is related to how people experience the clock changes this could result in biased estimates of the effects of the clock changes.
- Finally, the study could not analyse life satisfaction before and after the clock changes in the same people because participants only provided data before or after the clock change (not both).
Implications for practice
This study contributes to the substantial current debate surrounding daylight saving time policy. Research into the negative consequences of the transitions has resulted in many countries, including Russia, Mexico, Brazil and Iran ending the practice in the last 15 years. Most recently, the US and European Union are in the process of ending the clock changes.
The cost-benefit analysis conducted by the authors provides useful and unique evidence base for policy makers interested in the wider mental health effects of the clock changes not captured in routine health records. However, it is not clear whether the 1.4% decline in life satisfaction after the Spring clock change is meaningful on a practical or clinical level. For example, would participants have noticed this change themselves (if not asked specifically about it) and is the difference big enough to negatively impact those at risk for certain mental health conditions? Future research could use self-report data linked to people’s medical records to explore this.
The cost-benefit analysis conducted in this study provides a valuable evidence base for policy makers.
Statement of interests
No conflicts of interest to declare.
Links
Primary paper
Costa-Font, J., Fleche, S. & Pagan, R. (2024). The welfare effects of time reallocation: evidence from Daylight Saving Time. Economica, 91(362), 547-568.
Other references
Havranek, T., Herman, D. & Irsova, Z. (2018). Does Daylight Saving Save Electricity? A Meta-Analysis. The Energy Journal, 39(2), 35-62.
Hansen, B. T., Sønderskov, K. M., Hageman, I., Dinesen, P. T. & Østergaard, S. D. (2017). Daylight savings time transitions and the incidence rate of unipolar depressive episodes. Epidemiology, 28(3), 346-53.
Lindenberger, L. M., Ackermann, H. & Parzeller, M. (2019). The controversial debate about daylight saving time (DST)-results of a retrospective forensic autopsy study in Frankfurt/Main (Germany) over 10 years (2006-2015). International Journal of Legal Medicine, 133(4), 1259-65.
Kuehnle, D. & Wunder, C. (2014). Using the life satisfaction approach to value daylight savings time transitions: Evidence from Britain and Germany. BGPE Discussion Paper, No. 156, Friedrich-Alexander-Universität Erlangen-Nürnberg, Bavarian Graduate Program in Economics (BGPE), Nürnberg.
Moscoe, E., Bor, J. & Bärnighausen, T. (2015). Regression discontinuity designs are underutilized in medicine, epidemiology, and public health: a review of current and best practice. Journal of Clinical Epidemiology, 68(2), 132-43.
