In one line: Bias is anything that pulls research away from the truth.
You already know how bias works.
Picture watching a match next to someone who supports the other team. The same tackle goes in: you see a clear foul, they see a fair challenge.
Neither of you is lying. You each honestly notice the version that fits what you already believe.
Researchers are people too. What they hope to find can quietly shape a study, without them ever meaning it to.
In psychology, bias is any influence that stops research being objective. It works like a filter made of a person's own experience and preferences.
Bias can be out in the open (explicit: the person knows about it) or hidden (implicit: the person does not notice it). Most bias in research is the hidden kind.
Remember: Bias = a filter on the truth.
It is not lying. It is an honest tilt in what we see or report.
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Key idea: Bias comes from three places: how the study is set up (the design), the researcher, and the participants.
Imagine a study asking: does a new energy drink make people run faster?
Watch how bias could creep in from each place.
Sampling bias (design)
The people studied do not represent the wider group.
Here: only keen runners who already love energy drinks volunteer, so the result may not apply to anyone else.
When the people who say no are different from those who say yes, it is called non-response bias.
Leading questions (design)
The wording of a question pushes people towards one answer.
Here: the form asks "How much faster did the drink make you?" instead of "Did your speed change?"
Researcher bias
The researcher's hopes shape how they run or read the study.
Here: the drink company is paying, and the researcher cheers on the runners who had the drink.
In an interview this is called interviewer bias: a nod or a smile shows people which answers please the researcher.
Confirmation bias (researcher)
Noticing what fits your expectation and ignoring what does not.
Here: the researcher counts every fast run as proof, but explains away the slow ones as "just a bad day".
Publication bias (researcher)
Mostly positive results get published.
Here: "Energy drink boosts speed!" gets printed. The ten studies where it did nothing stay in a drawer, unseen (the file-drawer problem).
Participant bias
People act differently because they know they are being studied.
Here: the runners push harder than they normally would, simply because someone is standing there timing them. Trying harder just because you are in a study is called the Hawthorne effect.
Exam tip: Name the type, then say how it would affect this study.
"There is bias" says little. "Sampling bias means the result only applies to keen runners" says exactly what went wrong.
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Key idea: People change when they know they are in a study. This is also called participant expectations, and it has three named forms.
Go back to the energy-drink runners. Each one knows a researcher is watching, and each one answers questions afterwards.
Three forms of participant bias
Demand characteristics
Clues in the study let people guess the aim, and they act to fit it.
Here: the runners see the drink's logo on the stopwatch, guess that fast times are wanted, and sprint.
Social desirability
People give the answer that makes them look good. It is one kind of response bias.
Here: asked how often they train, runners say "every day" because it sounds better than the truth.
Recall bias
People misremember the past without meaning to.
Here: asked what they ate and drank last week, runners guess, and some of the guesses are wrong.
Guess the aim · Look good · Misremember
Tell them apart: Guessed the aim? Demand characteristics.
Wants to look good? Social desirability.
An honest memory slip? Recall bias.
How this is asked: You are asked to explain bias in a study you ran yourself: your class practical. It is a short answer for 4 marks.
Your class practicals
- Your class runs four small studies of its own, called class practicals.
- They are 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.
The answer pattern
- Say what bias is, in one sentence.
- Name one bias and show where it entered your practical.
- Name a second bias and do the same.
- Say what the two biases do to the conclusion.
The trap: bias in general: A list of bias types with no practical in it stays in the lower half of the marks.
Every bias you name needs a detail from what your class actually did.
Your class practical was a questionnaire. Twenty students from your own psychology class answered ten questions about how many energy drinks they have each week and how well they sleep. Explain the concept of bias in relation to the questionnaire in your class practical.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.