Are you looking for reliable health information? Would you like to know more about health apps before you use them? The Health Science research unit of the Zurich University of Applied Sciences (ZHAW) has been commissioned by AXA healthcare to draw up scientifically-based health information and tips on a variety of health topics. It selects and evaluates apps that can provide you with support in these health issues. Please see the Methodology section below for details on how we arrive at these evaluations.
What happens during sleep?
Adults spend around a third of their lives asleep. But why do we sleep at all, and what happens while we are asleep?
Sleep – supposed rest?
The nocturnal hormone melatonin forms during darkness. It regulates the day/night rhythm and is what causes us to feel tired in the first place. During sleep the autonomic nervous system relaxes. Our breathing rhythm becomes flatter, and blood pressure, pulse and body temperature fall. Yet during this resting mode, other bodily functions work at full throttle: Part of the digestive process takes place during sleep. Various hormones are released, or reach their peak, at night. For example, the hormone leptin stops us from feeling hungry during the night.
Latest findings from sleep research: The washing machine in the brain
The latest scientific findings indicate that spinal fluid flows around our brain in rhythmic waves during sleep, where it cleans the brain of harmful metabolites. While we calmly slumber on, our brains may be undergoing a kind of washing cycle.
Why is sleep so important?
An adequate amount of sleep strengthens the immune system and lowers the risk of suffering from high blood pressure or type 2 diabetes. Our psychological well-being and cognitive performance are also improved by sufficient sleep. After a restful night, we have stronger nerves. We become calmer and more alert during the day.
Important fact for drivers:
Sufficient sleep increases road safety. After a sleepless night, our reaction times become slower. The ability to drive of those who have had little sleep is comparable with that of people who are under the influence of alcohol. Anyone who has not slept at all during the night is advised not to get behind the wheel.
Did you sleep well?
Restful and healthy sleep is characterized by a sufficient duration of sleep and a good quality of sleep.
How many hours of sleep do we need?
First of all, there is no "magic number"! The duration of sleep required varies from person to person and is influenced by our genes. While short sleepers feel fit and rested after less than six hours’ sleep, long sleepers need nine hours or more. In Switzerland, the average duration of sleep on a working day is around seven and a half hours. But most would prefer to sleep for longer, because the average period asleep rises to eight and a half hours on days off.
Not sleeping sufficiently for one night isn't a problem, since this can be made up at the weekend. But if people repeatedly get too little sleep, the acute sleep deficit can have adverse effects on the mind and body.
What is good sleep quality?
If you wake up feeling refreshed in the mornings, are generally satisfied with your sleep and feel neither tired nor inattentive during the day, then you probably enjoy good sleep quality.
Stressful situations, stress at work and in one's private life, or health problems can impair the quality of sleep. Everyone experiences a poor night's sleep from time to time. Long-term sleeping disorders usually place a heavy burden on the sufferers. Sleeping problems that persist for longer than three months require medical investigation. While sustained sleeping disorders are often connected with physical or mental health problems, they can also occur without any underlying illness.
How well do young adults sleep in Switzerland?
Sleeping disorders are also fairly common in young people in Switzerland. A good third of 15 to 34-year-olds experience problems with falling or staying asleep. People do not sleep equally well in all regions of the country. In French and Italian-speaking Switzerland, the percentage of people who have problems falling or staying asleep (45.1%) is higher than in the German or Romansh-speaking parts of the country (38.5%).
What can I do about sleep problems?
Sometimes little needs to be done in order to sleep better, other times rather more is required.
If you want to improve your sleep, you can try various courses of action: Change your behavior using different behavior modification techniques, question your thought processes, employ relaxation techniques and follow general sleep hygiene rules. From the scientific standpoint, combining these various approaches is more promising than just following a single strategy. Trying out and combining strategies is worthwhile.
The combination of the above-mentioned approaches is technically known as "cognitive behavioral therapy for insomnia". It is considered to be an effective method for problems with falling or staying asleep. 
Sleeping tips to try out and combine
The bed, the best sleeping aid: Stimulus control
One possible behavior modification technique is stimulus control. Here are two tips for implementing this technique.
- Use your bedroom only for sleeping
People who are unable to fall asleep often distract themselves by lying in bed with their cell phone or laptop. Doing anything in the bedroom other than sleeping disrupts the mental association "bedroom = sleep". The bedroom or the bed is no longer perceived to be a sleep-promoting stimulus. In order to restore this stimulus, i.e. the mental association "bedroom = sleep", the bedroom should be used only for sleeping.
- Go to bed only when you are tired. If you do not fall asleep within 20 minutes, get out of bed
If you are unable to fall asleep within 20 minutes of going to bed, or are awake for longer than 20 minutes during the night, leave the bedroom and do something restful (e.g. read a book) until you are tired. Only then should you go back to bed. Even if your sleep is interrupted several times during the night, it is important for you to get up at the usual time in the morning and avoid taking any naps during the day.
Stimulus control is an integral part of cognitive behavioral therapy for insomnia. Population studies indicate that stimulus control, even when used on its own, can produce an effect and improve sleep,    particularly in those who have problems falling asleep. Consequently, this method does not necessarily have to be combined with the other strategies of cognitive behavioral therapy for insomnia. Give it a try.
Lying awake in bed is pointless: Sleep restriction
Lying in bed staring at the ceiling and failing to fall asleep is frustrating.
- Shorten your time in bed to your actual sleeping time
In sleep restriction, the time spent in bed is reduced to the time spent actually sleeping. If you lie in bed every night for eight hours, but only sleep for five of these hours, you should reduce your time in bed to five hours. Sleep through the night again and gradually lengthen your time in bed until you have reached your desired duration of sleep. Please note: Shortening your sleeping time can temporarily aggravate daytime fatigue and problems with concentration and attentiveness.
Rid yourself of sleep-robbing thoughts
Negative thoughts can make it more difficult to fall and stay asleep.
- Write down your problems, worries and distracting thoughts
You should avoid taking your problems and worries from your everyday life with you to bed, because problems that are suppressed during the day can become exasperating nuisances at night. That's why it is advisable to deal with your worries and problems during the course of the day and then write these down in a list or a journal.
- Try to develop a positive relationship with your sleep
A growing fear of sleeplessness increases tension, which in turn delays the onset of sleep. You can break this vicious circle by being aware of, and questioning, your negative thoughts about sleep. Do you really sleep badly every night? A poor night with little sleep is often followed by a good night due to the increased sleep pressure. Reassure yourself with the thought that the next night will be better.
Relaxed sleeping thanks to relaxation
Since sleeping problems are often associated with increased physical and/or mental tension, relaxation techniques serve as an effective supplement to the other approaches of cognitive behavioral therapy for insomnia.
- Use relaxation techniques specifically for releasing tension
Deliberate and active physical relaxation can be achieved, for example, using muscle relaxation techniques such as autogenic training, progressive muscle relaxation or yoga. Mindfulness exercises or meditation techniques can help you relax mentally.
A new take on traditional wisdom: Sleep hygiene rules
Sleep hygiene rules are general recommendations on how to behave in order to sleep well.
- Do not consume any caffeine-containing drinks in the evening
Studies indicate that moderate or heavy caffeine consumption up to six hours before going to bed can be detrimental to sleep. Whether coffee taken even early in the morning interferes with sleep at night has not yet been adequately clarified. Individual factors, such as a person's sensitivity to caffeine or the frequency of caffeine consumption during the day, also influence the quality of sleep.
- Do not consume alcohol before going to bed
Although alcohol is used by some "for medicinal purposes" to help with problems falling asleep, the consumption of alcohol before going to bed is not recommended. Although one or two glasses of wine can help you fall asleep faster, it also adversely affects the quality of your sleep. The resulting sleep is lighter and you will wake more often during the night. 
- Avoid nicotine
The consumption of nicotine in the form of cigarettes, nicotine tablets or nicotine plasters, particularly in large amounts, affects sleep quality. Although tolerance effects also exist, many smokers report sleeping problems and shorter duration of sleep. In smokers, nicotine withdrawal can lead to a temporary worsening of sleep. 
- Exercise during the day
Regular training as well as individual exercise sessions have a positive impact on sleep.  Moderate exercise can be undertaken less than four hours before going to bed without adversely affecting the sleep quality of healthy adults. By contrast, intensive training carried out less than one hour before going to bed will prolong the time taken to fall asleep and shorten the overall duration of sleep.
- Avoid bright light or blue light before going to bed
Studies have shown that the light from electronic devices affects our biorhythms and is detrimental to sleep.   Since blue light in particular lowers the production of the hormone melatonin, we take longer to feel tired after looking at a screen. Consequently, the use of blue-light filters is recommended. One way to do this is simply to switch your computer or cell phone screen to night mode in the evening. If you need glasses when viewing a screen, you can also try using spectacle lenses with an integrated blue-light filter.
- Eliminate disturbing noises or use earplugs
Loud music in the next room, a ticking alarm clock or even a snoring partner can disrupt your own night's rest. While loud music can be switched off and the ticking alarm clock replaced by a silent model, other sources of noise cannot be removed so easily. Studies on intensive care units have shown that the use of earplugs can improve nocturnal sleep in noisy environments.
The Health Science research unit has evaluated a number of apps that can be helpful to you in respect of a particular health topic. The evaluation is based on the following categories.
A transparent app gives the potential user sufficient information on the use, objectives, costs, and data usage, along with an adequate site notice so that they can make an individual and collective usage decision.
- Expediency (incl. change in behavior)
An expedient app contains functions that are appropriate for the envisaged purpose. The evaluation of the expediency of these apps is based on the use of recognized behavioral change techniques.
- Risk appropriateness
A risk-appropriate app can be used without the user or those close to them being exposed to any disproportionate health, social, or economic risk. Aspects evaluated include low-risk default settings and access rights, along with information on reliability of diagnoses or recommendations.
- Ethical soundness
An ethically sound app takes into account ethical principles valid in Switzerland as well as standards of good scientific practice. Among other things, the protection of the individual’s private sphere and the separation of advertising and content has been reviewed.
- Technical appropriateness
An app is deemed to be technically appropriate if its development, operation, maintenance, and use corresponds to the latest state of technology and facilitates enduring maintainability and compatibility. Among other things, technical appropriateness was measured on the basis of technical reliability, possible operating systems, and data transfer options. Many aspects of technical appropriateness can only be evaluated and declared by the developer.
An app is deemed to have good usability if the software is appropriate to the target group in question and contributes to the user’s satisfaction. Aspects evaluated here include functionality, error messages, support options, and off-line usability.
- Health competence
An app is deemed to be health-competent if the language, measurement units, and recommendations are clear and comprehensible.
- Resource efficiency
An app is deemed to be resource-efficient if, during development, resource-efficient use has been taken into consideration, for example with regard to the use of electricity, storage capacity, or computing power. This category cannot be evaluated without prolonged use or developer information.
- Legal compliance
An app is deemed to be legally-compliant if it guarantees compliance with the legal situation, encompassing areas such as medical product law, professional law, or data protection law of the relevant operating countries. This category is not always applicable / cannot always be evaluated, and is only scrutinized in the case of medical product apps.
*Only the percentage of the fulfilled criteria is indicated
This app offers a sleep tracking function that records your sleep and calculates your “SleepScore”. The detailed sleep analysis takes account of four stages: light sleep, deep sleep, REM sleep and waking phases. With its light and noise measurement function you can check your sleeping environment. Other functions of the app include sleeping aids, a smart alarm function and sleeping tips.
- Advantages / Disadvantages
SleepScoreTM covers eleven behavioral change techniques. For example, you can define your own sleep goals and you get feedback about your sleeping behavior.
Sleep recording works without any additional hardware. So far it has been successfully tested on the following devices: Samsung Galaxy S7, S7 Edge, S8, S8+, S9, S9+, Note 8, Note 9, and Google Pixel 2 XL.
The app cannot be reliably used on every device. According to the manufacturers, the app has not been tested on the following devices: iPad, iPod Touch, iPhone 5s, and iPhone SE. Sleep recording only works when the charger is connected. In addition, the individual sleep phases are not (yet) reliably measured, but the measurements can be used as a guide.
App Peak Sleep
*Only the percentage of the fulfilled criteria is indicated
This app offers eight scientifically supported methods to improve sleep. Mindfulness meditation, guided imagery, progressive muscle relaxation, acceptance and commitment therapy, cognitive behavior therapy, calming music, sounds of nature, and breathing exercises. You can check your sleeping progress with an integrated sleep diary.
- Advantages / Disadvantages
Peak Sleep includes various behavioral change techniques. For example, you get a free audio introduction recorded by experts for each method. The app also provides what is known as a “ritual” each day: a sleep diary entry, a guided relaxation/therapy unit. After gaining this initial impression, you decide for yourself whether it is worthwhile for you to buy the entire package
The App Store description does not make it clear that the whole sleep improvement program and the full statistics from the sleep diary are only accessible after buying a monthly or an annual subscription.
App Sleep Cycle
*Only the percentage of the fulfilled criteria is indicated
**Criteria not applicable
Language: German, English, French, Italian
The aim of Sleep Cycle is to improve the general quality of your sleep. To this end the app offers a sleep aid. A sleep tracking function records your sleep and with the smart alarm function you can be woken in light sleep phases.
- Advantages / Disadvantages
Sleep Cycle covers three behavioral change techniques. For example, you can check with the aid of the sleep recordings whether your sleep is improving over time.
Sleep recording works without any additional hardware. The device can be placed on the bedside table or on the mattress and it records your sleep by means of a microphone and an accelerometer.
There are no details about the accuracy of the sleep recordings or the calculation of the various sleep phases. The sleep phases recorded in the app do not always correspond with actual sleep at night, which limits the functionality of the sleep phase alarm. Sleep recording consumes a lot of battery. Although the app can be used in three languages, some app functions and the support information are only available in English.
*Only the percentage of the fulfilled criteria is indicated
**Criteria not applicable
Language: German, French, English
With Calm you can learn meditation techniques. To conquer your sleep problems, the app also offers sleep stories, breathing programs, and calming music.
- Advantages / Disadvantages
Calm covers nine behavioral change techniques. For example, meditation exercises are supported by audio material from meditation coaches, you can repeat the meditation exercises several times and you receive positive feedback in the form of a congratulation message.
Breathings exercises and mood pictures with sounds of nature are freely accessible. You can try out the first day of each of the seven-day meditation programs free of charge. After gaining this initial impression, you decide whether it is worthwhile for you to buy the entire meditation program
Information about the scope of the free offer is not to be found in the App Store. You don’t get a complete overview of the free offer until you visit the app provider’s website.
Methology – evaluation and selection
- How did we arrive at the app criteria?
Where the catalog of criteria for the evaluation of apps is concerned, we have focused on three key resources.
- “Einheitlichen Kriterienkatalog zur Selbstdeklaration der Qualität von Gesundheits-Apps” [Standardized catalog of criteria for self-declaration of quality of healthcare apps]"
This catalog drawn up by ehealthsuisse, the relevant center of competence and coordination for the Confederation and cantons in Switzerland, formulates nine categories for quality review, of which we have used seven for the purposes of our evaluation criteria. The two criteria not taken into account were “resource efficiency” and “legal compliance”, as these are only partially applicable or reviewable. The category “health competence” was newly created by the Health Science research unit.
- “APPKRI-Kriterien für Gesundheits-Apps” [APPKRI criteria for health apps”], drawn up by the Fraunhofer Institute for Open Communication Systems"
These app evaluation criteria have been developed on behalf of the Federal Ministry of Health in Germany. This meta-criteria catalog currently encompasses 290 criteria and forms the basis for our evaluation criteria. The ZHAW research team has identified 56 criteria as key to the app evaluation process.
- “The behavior change technique taxonomy” by Susan Michie and colleagues (2013)"
One focus of our app evaluation is the techniques of behavior change. When evaluating the “Expediency” category, the 93 behavior techniques of this taxonomy were reviewed for their use in the app. For example, the display of sleep duration by a sleep analysis app constitutes a form of “behavior feedback” and therefore a recognized behavior change technique.
- How have we evaluated the app criteria?
- The criteria have been evaluated with yes (applies) or no (does not apply) and irrelevant. The evaluations of the individual criteria for each app are available in PDF form.
- The bar charts correspond to the percentage proportions of the criteria per category that were evaluated with a “yes” or “no”. Only applicable criteria are used in the calculation.
- The stars correspond to the aggregated total of the criteria answered with “yes” across all categories, e.g. four stars means that 80% of the evaluated criteria were answered with “yes”.
- How did we arrive at our app selection?
We identified apps through the program 250 using topic-specific search terms. On the basis of various features we then made a pre-selection from the large pool of apps identified. The apps that you can find on the website also reflect the multiplicity of methods and approaches common in the healthcare area.
Selected apps had to…
- be offered both for the iOS and Android operating systems,
- exhibit a full site notice,
- only request access to the personal data needed for use of the app,
- require no additional hardware.
- offer privacy protection settings,
- be usable without a permanent internet connection,
- list both the function and price of in-app purchases,
- specify the scope and duration of usage rights,
- stipulate the usage scenarios for which the app is not suitable,
- not impair usage significantly through pop-up advertising or similar,
- function flawlessly and reliably,
- not offer any incentives to pass on personal or third-party data,
- lag up any incorrect use as risky,
- clearly define the goal achievable through use of the app in the App Store,
- and use language that would be readily comprehensible to the target group.
The content on the subject of sleep was scientifically compiled by the ZHAW. The commission for this and the financing was provided by AXA.
1. Grandner, M. (2019). Sleep and health (1st edition). San Diego, CA: Elsevier.
2. Fultz, N. E., Bonmassar, G., Setsompop, K., Stickgold, R. A., Rosen, B. R., Polimeni, J. R., & Lewis, L. D. (2019). Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science, 366(6465), 628–631. https://doi.org/10.1126/science.aax5440
3. Guo, X., Zheng, L., Wang, J., Zhang, X., Zhang, X., Li, J., & Sun, Y. (2013). Epidemiological evidence for the link between sleep duration and high blood pressure: A systematic review and meta-analysis. Sleep Medicine, 14(4), 324–332. https://doi.org/10.1016/j.sleep.2012.12.001
4. Holliday, E. G., Magee, C. A., Kritharides, L., Banks, E., & Attia, J. (2013). Short Sleep Duration Is Associated with Risk of Future Diabetes but Not Cardiovascular Disease: A Prospective Study and Meta-Analysis. PLoS ONE, 8(11), e82305. https://doi.org/10.1371/journal.pone.0082305
5. Powell, N. B., Schechtman, K. B., Riley, R. W., Li, K., Troell, R., & Guilleminault, C. (2001). The road to danger: The comparative risks of driving while sleepy. The Laryngoscope, 111(5), 887–893. https://doi.org/10.1097/00005537-200105000-00024
6. Tinguely G., Landolt H.-P. & Cajochen, C. (2014) Schlafgewohnheiten, Schlafqualität und Schlafmittelkonsum der Schweizer Bevölkerung – Ergebnisse aus einer neuen Umfrage bei einer repräsentativen Stichprobe. Therapeutische Umschau 71(11): 637-646.
7. Taylor, D. J., Lichstein, K. L., & Durrence, H. H. (2003). Insomnia as a Health Risk Factor. Behavioral Sleep Medicine, 1(4), 227–247. https://doi.org/10.1207/S15402010BSM0104_5
8. OBSAN (2019) Einschlaf- oder Durchschlafstörungen. Abgerufen am 4. Dezember 2019, von https://www.obsan.admin.ch/de/indikatoren/einschlaf-oder-durchschlafstoerungen
9. Murawski, B, Wade, L. Plotnikoff, R., Lubans, D.R., Duncan, M. (2018) A systematic review and meta-analysis of cognitive and behavioral interventions to improve sleep health in adults without sleep disorders. Sleep medicine Reviews 40: 160-169.
10. Riemann, D., Baglioni, C., Bassetti, C., Bjorvatn, B., Groselj, L. D., Ellis, J. G., …& Spiegelhalder, K. (2017). European guideline for the diagnosis and treatment of insomnia. Journal of Sleep Research, 26(6), 675–700. https://doi.org/10.1111/jsr.12594
11. Qaseem, A., Kansagara, D., Forciea, M. A., Cooke, M., Denberg, T. D., & Clinical Guidelines Committee of the American College of Physicians. (2016). Management of Chronic Insomnia Disorder in Adults: A Clinical Practice Guideline From the American College of Physicians. Annals of Internal Medicine, 165(2), 125–133. https://doi.org/10.7326/M15-21712
12. Brasure, M., MacDonals, R., Fuchs, E., Olson, C. M., Carlyle, M., Diem S., Koffel E., Khawaja I. S., Oulette, J., Buttler M., Kane, R. L. & Wilt T. J. (2015). Management of Insomnia Disorder. AHRQ Publication No. 15.
13. Chesson, A. L., Anderson, W. M., Littner, M., Davila, D., Hartse, K., Johnson, S.,…& Rafecas, J. (1999). Practice parameters for the nonpharmacologic treatment of chronic insomnia. An American Academy of Sleep Medicine report. Standards of Practice Committee of the American Academy of Sleep Medicine. Sleep, 22(8), 1128–1133. https://doi.org/10.1093/sleep/22.8.1128
14. Bootzin, R. R., & Perlis, M. L. (2011). Chapter 2—Stimulus Control Therapy. In M. Perlis, M. Aloia, & B. Kuhn (Hrsg.), Behavioral Treatments for Sleep Disorders, 21–30. https://doi.org/10.1016/B978-0-12-381522-4.00002-X
15. Sidani, S., Epstein, D. R., Fox, M., & Collins, L. (2019). Comparing the Effects of Single- and Multiple-Component Therapies for Insomnia on Sleep Outcomes. Worldviews on Evidence-Based Nursing, 16(3), 195–203. https://doi.org/10.1111/wvn.12367
16. Murawski, B., Wade, L., Plotnikoff, R. C., Lubans, D. R., & Duncan, M. J. (2018). A systematic review and meta-analysis of cognitive and behavioral interventions to improve sleep health in adults without sleep disorders. Sleep Medicine Reviews, 40, 160–169. https://doi.org/10.1016/j.smrv.2017.12.003
17. Drake, C., Roehrs, T., Shambroom, J., & Roth, T. (2013). Caffeine Effects on Sleep Taken 0, 3, or 6 Hours before Going to Bed. Journal of Clinical Sleep Medicine, 9(11), 1195–1200. https://doi.org/10.5664/jcsm.3170
18. Irish, L. A., Kline, C.E., Heather, E. G., Buysse, D. J., & Martica H. (2015) The Role of Sleep Hygiene in Promoting Public Health: A Review of empirical Evidence. Sleep Medicine Reviews, 22: 23-36.
19. Jaehne, A., Loessl, B., Bárkai, Z., Riemann, D., & Hornyak, M. (2009). Effects of nicotine on sleep during consumption, withdrawal and replacement therapy. Sleep Medicine Reviews, 13(5), 363–377. https://doi.org/10.1016/j.smrv.2008.12.003
20. Patterson, F., & Ashare, R. (2019). Chapter 22—Improved sleep as an adjunctive treatment for smoking cessation. In M. A. Grandner (Hrsg.), Sleep and Health (S. 283–301). https://doi.org/10.1016/B978-0-12-815373-4.00022-8
21. Lowe, H., Haddock, G., Mulligan, LD., Gregg, L., Fuzellier-Hart, A., Carter, LA. & Kyle, SD. (2019) Does exercise improve sleep for adults with insomnia? A systematic review with quality appraisal. Clinical Psychological Review, 68:1-12.
22. Stutz, J., Eiholzer, R., & Spengler, C. M. (2019). Effects of Evening Exercise on Sleep in Healthy Participants: A Systematic Review and Meta-Analysis. Sports Medicine, 49(2), 269–287. https://doi.org/10.1007/s40279-018-1015-0
23. Green, A., Cohen-Zion, M., Haim, A. & Dagan, Y. (2018). Comparing the response to acute and chronic exposure to short wavelength lighting emitted form computer screens. Journal of Biological and Medical Rhythm Research 35(1).
24. Green, A., Cohen-Zion, M., Haim, A. & Dagan, Y. (2017). Evening light exposure to computer screens disrupts human sleep, biological rhythms, and attention abilities. Chronobiology International, 34(7): 855-865.
25. Chang, A.-M., Duffy, J. F. & Czeisler, C. A. (2015) Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences 112(4): 1232-1237
26. Kimberly, B., & R, P. J. (2009). Amber Lenses to Block Blue Light and Improve Sleep: A Randomized Trial. Chronobiology International, 26(8), 1602–1612. https://doi.org/10.3109/07420520903523719
27. Muzet, A. (2007). Environmental noise, sleep and health. Sleep Medicine Reviews, 11(2), 135–142. https://doi.org/10.1016/j.smrv.2006.09.001
28. Xie, H., Kang, J., & Mills, G. H. (2009). Clinical review: The impact of noise on patients’ sleep and the effectiveness of noise reduction strategies in intensive care units. Critical Care, 13(2), 208. https://doi.org/10.1186/cc7154