Demand Characteristics & Investigator Effects
Applied Science: BTEC Level 3 National Extended Diploma, topic 3.1.5
Experimenter Bias
Experimenter bias is the risk that an experimenter might affect the results of the study. Experimenter bias and the placebo effect can be accounted for using double-blind trials.
Experimenter bias
- Experimenter bias refers to the possibility that a researcher’s expectations might skew the results of the study.
- Remember, conducting an experiment requires a lot of planning, and the people involved in the research project have a vested interest in supporting their hypotheses.
Single- vs double-blind studies
- In a single-blind study, one of the groups (participants) are unaware as to which group they are in (experiment or control group) while the researcher who developed the experiment knows which participants are in each group.
- In a double-blind study, both the researchers and the participants are blind to group assignments.
- This is useful because by doing so, we can control for both experimenter and participant expectations.
The placebo effect
- The placebo effect happens when people's expectations or beliefs influence or determine their experience in a given situation.
- In other words, simply expecting something to happen can actually make it happen.
- The placebo effect is commonly described in terms of testing the effectiveness of a new medication.
The placebo effect - depression drugs
- In the case of testing a drug for depression, for example, a participant taking a pill that they expect will improve their mood might feel better simply because they took the pill and not because of any drug actually contained in the pill - this is the placebo effect.
Controlling for the placebo effect
- To control for the placebo effect, one group will receive the real drug and one group will receive a sugar pill and neither the participant nor the experimenter will know which pill they took.
- The improvements can then be tested between the groups and the control group with the placebo effect can be treated as a baseline.
Test yourself on Demand Characteristics & Investigator Effects
What do we call it when a participant makes an improvement despite NOT being given a treatment?
Whose expectations are controlled for in a single blind study?