The Hawthorne effect refers to the phenomenon whereby participants alter their behaviour because they know they are being studied, not because of the experimental treatment itself. Any observed improvement may reflect the novelty of participation, increased attention, or awareness of being observed rather than the independent variable.
The term derives from a series of studies conducted at the Western Electric Company's Hawthorne Works in Cicero, Illinois (1924-1933). Researchers (including Elton Mayo) manipulated working conditions, including lighting, rest periods, and hours, and found that productivity improved regardless of the specific change. The explanation offered was that workers performed better because they were receiving attention and knew they were being observed. J.R.P. French (1953) coined the term "Hawthorne effect" to describe this phenomenon.
The original studies have been heavily criticised: Levitt & List (2011) re-analysed the data and found that the supposedly dramatic patterns were overstated. Nevertheless, the concept remains a standard validity threat in experimental research.
The Hawthorne effect is a significant confound in SLA classroom studies:
The Hawthorne effect overlaps with several Internal Validity threats: it resembles the testing effect (awareness changes behaviour), novelty effect (new methods seem exciting), and the Observer's Paradox (observation changes the phenomenon). Distinguishing between these requires careful design and transparent discussion.