Observer-Expectancy Effect
Researchers unconsciously influence experiments by communicating their expectations to participants.
The observer-expectancy effect (also experimenter expectancy effect) occurs when a researcher's cognitive bias causes them to unconsciously influence the participants of an experiment. Expectations subtly change body language, tone, and experimental administration. This effect is controlled by double-blind procedures in clinical trials; without them, even honest researchers can produce biased results.
What it looks like in the wild.
- Science Clever Hans A horse appeared to do arithmetic, but was actually reading subtle, unconscious cues from its trainer who expected a specific answer — a classic demonstration of observer-expectancy bias.
Recognising a definition is not the same skill as spotting it.
Two scenarios from the app, with distractors drawn from the same family of biases — which is what makes them hard.
A researcher, expecting a specific outcome, explains the study's potential to participants in an upbeat tone. The participants' responses align with the researcher's hypothesis.
A parent who expects their child to be picky about food serves new dishes with a hesitant expression. The child, picking up on the cue, refuses to try the food, confirming the parent's belief.
Biases rarely arrive alone.
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