The Hawthorne effect occurs when people behave differently because they know they are being watched.
It can affect all sorts of behaviours such as dietary habits, or hygiene practices because these have considerable opportunity for instantaneous modification. It can also affect study results, e.g. a survey of smoking by watching people during work breaks might lead to observing much lower smoking rates than is genuinely representative of the population under study. It can also contaminate an intervention study if one of the control groups changes its behaviour because it is being observed more frequently than the other.
The original Hawthorne study looked at changing the amount of light at the Hawthorne Works and its impact on working practices. The increased attention focussed on the workers as part of the study led to temporary increases in production (the Hawthorne effect) as opposed to changes in working practices
The Hawthorne effect can also lead to the observation being the intervention. For example, recommending individuals who want to lose weight should keep a diary of what they eat and drink.
A study of hand-washing among medical staff found that when the staff knew they were being watched, compliance with hand-washing was 55% greater than when they were not being watched (Eckmanns 2006).
In a study of dementia patients, more intensive follow-up (comprehensive assessment visits at baseline and 2, 4 and 6 months) in a clinical trial of Ginkgo biloba resulted in a better cognitive functioning outcomes than minimal follow-up (abbreviated assessment at baseline and full assessment at 6 months). (McCarney R 2007)
A systematic review investigating the impact of the Hawthorne effect identified 19 studies evaluating the behaviour of participants aware they were being studied (McCambridge 2014). These 19 studies showed a wide range of variation in the proposed Hawthorne effect, and no summary of the overall impact of the Hawthorne effect could be calculated. Nevertheless, the authors stated that “research participation can and does influence behaviour, at least in some circumstances.”
Another study examined the magnitude of the Hawthorne effect on compliance with a hand-hygiene protocol and collected alcohol hand-rub dispensers electronically (so that participants would not be aware of being observed or measured) as well as by human observers (Hagel 2006). The study recorded five hand hygiene events per patient per hour during periods of observation and two hygiene events per patient per hour in the periods without observation – 61% of the observed total variability in hand hygiene events was explained by the presence or absence of a direct observer – the Hawthorne effect.
Studies using hidden observation can help avoid the Hawthorne effect, although even knowledge of participation in a study per se is thought to have the potential to induce a Hawthorne effect (Persell 2016).