The Unexpected Benefits of Being Observed

Most public pools have lifeguards for a good reason. A lifeguard can save swimmers from drowning and discourage unsafe behavior. On top of this, because swimmers know they’re being watched, a lifeguard may prevent them from running on the pool deck, diving in the shallow end, and getting into other risky situations in the first place.

This situation is an example of the Hawthorne effect, a psychological phenomenon that describes how people change their behavior when they know they’re being observed.^[1] It gets its name from a study in an Illinois factory from the 1920s in which the effects of light on workers was measured in order to determine the effect of light on productivity. The study found that brighter lighting increased productivity (as expected).^[1] Contrary to the researchers’ predictions, however, dimming the lights also increased productivity.^[1] They concluded that this was not due to the effect of lighting at all, but instead an increase in productivity when workers knew the researchers were paying attention to them.^[2]

The Hawthorne effect applies to more situations than just factory work. It is also sometimes informally known as the “trial effect”.^[3,4] This is where the participants of a clinical trial perform better than the general population. This happens even when researchers control for the placebo effect, where taking a placebo or fake medication with no active ingredient can cause mild improvement.^[3] In one study, dementia patients showed less cognitive decline when they were more intensely monitored after treatment.^[5] In a meta-analysis of several cancer and asthma studies, patients had better outcomes simply by being in a study, whether they ended up taking an investigational drug or not.^[6]

The Hawthorne effect also benefits patients in weight loss studies. Many patients enroll in these studies with the objective of getting an investigational medication. Surprisingly, the data show that patients who do not receive a medication still lose some weight, on average.^[7] Furthermore, participants with obesity found significant improvements in both quality-of-life and biochemical markers while enrolled in sleep studies, even without administration of any treatment^[8]

The strength of this effect, albeit variable, is hard to discount. One aspect of the Hawthorne effect is the profound psychological impact of observation; when people know they are being monitored and held accountable, they tend to do better.^[9] Another important factor is the increased level of medical attention that accompanies participation in a clinical trial. Patients are regularly monitored by a team of physicians, nurses, and other healthcare professionals who closely track their health and progress. This heightened oversight may reinforce accountability, but it also allows researchers to identify and address important health issues that might otherwise go unnoticed. This dual accountability for both the participants and the researchers tends to result in better outcomes among clinical trial participants. The psychological effects of being observed and the clinical benefits of intensive monitoring reinforce each other, creating advantages for participants, regardless of whether they receive a study drug.

Acting Coordinator Daniel Benton 

References

[2] Mayo E. The Human Problems of an Industrial Civilization. Nature. 1933 Aug;134(3380):201–1. 

[3] Menezes P. Trial effect: the road from efficacy to effectiveness. Clinical Investigation [Internet]. 2012 May [cited 2026 July 21];2(5):443–5. Available from: https://www.ovid.com/journals/clni/abstract/10.4155/cli.12.34~trial-effect-the-road-from-efficacy-to-effectiveness

[4] Brody T. Chapter 7 - Placebo Arm as Part of Clinical Trial Design. In: Clinical Trials (Second Edition) [Internet]. Second Edition. Boston: Academic Press; 2016. p. 155–72. Available from: https://www.sciencedirect.com/science/article/pii/B9780128042175000072

[5] Hróbjartsson A, Gøtzsche PC. Is the Placebo Powerless? New England Journal of Medicine [Internet]. 2001 May 24 [cited 2026 July 21];344(21):1594–602. Available from: https://www.nejm.org/doi/full/10.1056/NEJM200105243442106

[6] Braunholtz DA, Edwards SJL, Lilford RJ. Are randomized clinical trials good for us (in the short term)? Evidence for a “trial effect.” Journal of Clinical Epidemiology [Internet]. 2001 Feb 19 [cited 2026 July 21];54(3):217–24. Available from: https://www.sciencedirect.com/science/article/pii/s089543560000305x

[7] Guo Y, Yang W, Lin C, Wu H, Li Z, Jiao R, et al. Placebo response on the weight change and its influencing factors in overweight or obesity with or without diabetes: a meta-analysis of 182 anti-obesity medications trials. Communications Medicine [Internet]. 2026 June 5 [cited 2026 July 21];. Available from: https://www.nature.com/articles/s43856-026-01659-7

[8] Cizza G, Piaggi P, Rother KI, Csako G. Hawthorne Effect with Transient Behavioral and Biochemical Changes in a Randomized Controlled Sleep Extension Trial of Chronically Short-Sleeping Obese Adults: Implications for the Design and Interpretation of Clinical Studies. Penzel T, editor. PLoS ONE. 2014 Aug 20;9(8):e104176. 

[9] Li Y, Liu W, Yu G. Dancing in Shackles: The Double-Edged Sword Effect of Felt Accountability on Work Outcomes and Individual Wellbeing. Frontiers in Psychology. 2022 June 10;13.