How can demand characteristics bias experimental results?

Demand characteristics can bias experimental results by influencing participants to alter their behaviour based on perceived expectations.

Demand characteristics refer to any aspect of an experiment that may reveal the purpose of the study or the experimenter's expectations, thereby influencing the participants' behaviour. This can lead to a bias in experimental results as participants may change their behaviour to align with what they believe the experimenter expects, rather than behaving naturally. This is often referred to as the 'good subject' tendency, where participants try to be 'good' or 'helpful' by confirming the experimenter's hypotheses.

For instance, if participants in a study on dietary habits are aware that the experiment is designed to promote healthy eating, they may report consuming more fruits and vegetables than they actually do. This could lead to an overestimation of healthy eating habits, thereby skewing the results. Similarly, in a study investigating the effects of a new teaching method, if students know that they are expected to perform better, they might work harder, not because of the new method, but because they want to meet the expectations. This could lead to an overestimation of the effectiveness of the teaching method.

Demand characteristics can also lead to a type of bias known as 'evaluation apprehension', where participants are concerned about being judged or evaluated. This can cause them to modify their behaviour in ways that they believe will be viewed favourably. For example, in a study on alcohol consumption, participants might under-report their drinking habits for fear of negative judgement.

To minimise the impact of demand characteristics, researchers often use single-blind or double-blind procedures. In a single-blind study, the participants do not know the purpose of the study or what is being tested. In a double-blind study, neither the participants nor the researchers know who is in the control group and who is in the experimental group. This helps to ensure that the results are not influenced by the participants' or researchers' expectations or biases. Despite these precautions, it is almost impossible to completely eliminate the influence of demand characteristics, but being aware of their potential impact can help researchers design and conduct more reliable and valid experiments.