In one line: Bias is a tilt away from the truth that the person usually cannot see in themselves.
Try this at home.
Pour the same cola into two cups. Put a famous brand's label on one and a supermarket label on the other. Most people say the famous one tastes better.
Nobody is pretending. The label changed what they honestly tasted.
A researcher's expectations work like that label. What she expects to find can change what she notices in her own study.
In psychology, bias is anything that makes research less objective.
When someone is aware of their bias it is explicit. When it works without them noticing, like the cola label, it is implicit. Implicit bias is the harder one to catch, because nobody feels it happening.
Remember: Bias is a filter, not a lie.
The tasters believed the label. Researchers believe their results.
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Key idea: Every bias starts in one of three places: the design of the study, the researcher, or the participants.
Take a study asking: does eating breakfast help students concentrate in morning lessons? A cereal company is paying for it.
Follow the bias through each place.
Sampling bias (design)
The sample does not match the group the study is about.
Here: the students who sign up already eat breakfast every day.
The students who skip breakfast ignore the invitation, so they are missing from the results. That gap is non-response bias.
Leading questions (design)
A question is worded so that one answer feels expected.
Here: "How much sharper do you feel after breakfast?" leaves no room for "no different".
Researcher bias
What the researcher hopes for shapes the running or reading of the study.
Here: she scores a borderline test as a pass for the breakfast group.
Face to face it becomes interviewer bias: she nods when a student praises breakfast, and students learn what to say.
Confirmation bias (researcher)
Taking in the evidence that fits and explaining away the rest.
Here: high scores after breakfast are "the effect". Low scores after breakfast are "a late night".
Publication bias (researcher)
Studies with a positive result are far more likely to be printed.
Here: "Breakfast boosts focus" is published. The company's three studies that found no difference are filed away (the file-drawer problem).
Participant bias
Knowing you are in a study changes how you behave.
Here: students told they are in "the breakfast study" try harder on the concentration test than they would in a normal lesson. That extra effort from simply being studied has a name: the Hawthorne effect.
Exam tip: Always ask who paid for the study and who is missing from the sample.
Those two questions find a bias in almost any piece of research.
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Key idea: Participant bias, also called participant expectations, is not one thing. It has three forms, and each has its own name.
Stay with the breakfast study. The students are given a free breakfast, then a concentration test, then an interview about their mornings.
Three forms of participant bias
Demand characteristics
Details of the study give the aim away, and people behave to match it.
Here: a test straight after a free breakfast makes the aim obvious, so students concentrate harder than usual.
Social desirability
People choose the answer that shows them in a good light. It is a type of response bias.
Here: asked what they normally eat, students say "fruit and cereal", not "nothing" or "crisps".
Recall bias
Memory of the past is incomplete, and the gaps get filled with guesses.
Here: asked what they ate each morning last week, students cannot remember and write down a typical week.
Work out the aim · Protect your image · Get the past wrong
Tell them apart: Acting on the aim? Demand characteristics.
Protecting an image? Social desirability.
Memory filled in with a guess? Recall bias.
Your four class practicals
- Your class runs four small studies of its own, called class practicals: an experiment, an interview, an observation and a survey.
- Paper 2 asks about the ones your class ran.
- Keep a short note of each: aim, what you did, who took part, what you found, and the ethics.
How this is asked: The question is about your own class practical: explain the concept of bias in relation to it, for 4 marks.
Four moves, four short paragraphs
- Define bias in a sentence.
- Give one bias and the exact point where it got into your practical.
- Give another bias, again with its point of entry.
- State what this means for how far the findings can be trusted.
The trap: leaving the practical out: Correct definitions on their own stay in the lower half of the marks.
The marks above that are for clear, detailed links between each bias and your study.
Your class practical was a set of interviews. Each student interviewed one classmate for ten minutes about their morning routine and how alert they feel in the first lesson. Explain the concept of bias in relation to the interview in your class practical.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.