Sources of Bias, Designing and Interpreting Investigations
Bias in Psychological Research
Every psychological study aims to measure behaviour accurately, but many things can distort the data collected. A bias is a systematic error that pushes results away from the truth in a particular direction. Bias can come from the participant, from the researcher, or from how a study is designed. Learning to spot different sources of bias is essential for the research methods sections of both papers, and for evaluating the core studies you have learned across every topic.
Demand Characteristics and the Observer Effect
Participants are not passive — they often try to work out what a study is about. Demand characteristics occur when a participant picks up on clues in the environment, instructions or materials and adjusts their behaviour accordingly, either trying to help the researcher get the ‘right’ result or deliberately sabotaging it.
A related but distinct problem is the observer effect. This happens simply because participants know they are being watched, not because they have guessed the study’s aim. Someone who behaves more politely because a researcher is nearby is showing the observer effect, even if they have no idea what is being tested.
Demand characteristics = the participant guesses the study’s aim and changes behaviour to match or disrupt it. Observer effect = the participant changes behaviour simply because they know they are being watched, regardless of whether they know the aim.
Social Desirability Bias
In interviews and questionnaires, participants often want to be seen in a good light. Social desirability bias is the tendency to give answers that present the participant favourably rather than answering truthfully. For example, a participant asked how often they exercise may over-report their activity because they want to appear healthy, even in an anonymous survey.
Bias Built Into the Sample or the Study Design
Bias is not only about what a participant does during a study — it can be built in from the start, through who is studied and how conclusions are drawn.
Gender bias occurs when findings based mainly on one gender are generalised to everyone. A study using only male participants but presenting its conclusions as true of ‘people’ in general is gender biased.
Cultural bias happens when a researcher interprets behaviour using the norms of their own culture, ignoring that customs, values and social rules differ elsewhere. A behaviour seen as ‘abnormal’ in one culture might be entirely typical in another.
Age bias occurs when a study samples a narrow age range — for instance, only teenagers — but its conclusions are applied to all ages, ignoring the fact that behaviour, cognition and social experience change across the lifespan.
Experimenter Bias, Observer Bias and Bias in Questioning
Experimenter bias occurs when a researcher’s expectations about the outcome unconsciously affect how they run the study — for example, giving subtle hints, tone of voice or extra encouragement to participants in one condition without realising it.
Observer bias is closely related but specific to observational research: it happens when an observer’s expectations affect what behaviours they notice, categorise or write down, so the recorded data is less objective than the behaviour actually shown. Finally, bias in questioning occurs when the wording, tone or order of interview or questionnaire questions steers participants toward a particular answer — for example, a leading question that assumes the answer within the question itself.
The full set of biases you need for the exam: demand characteristics, observer effect, social desirability bias, gender bias, cultural bias, age bias, experimenter bias, observer bias, and bias in questioning. Each can affect a study’s validity in a different way, so name the specific bias rather than saying ‘the study was biased’.
Designing an Investigation
One of the two research methods tasks in your exam requires designing an investigation. This means writing a hypothesis, identifying variables, choosing an experimental design and sampling method, and describing how ethical guidelines would be followed — all applied to a specific scenario given in the question, not generic textbook description. When a question asks you to design a study to test for a particular bias, state clearly how your design would reduce or control that bias, for example by using a double-blind procedure to reduce experimenter bias.
Responding to a Novel Source
The other research methods task instead presents a novel source — a piece of unfamiliar research information, such as a description of a study or a set of results, that you have not seen before. You must apply your research methods knowledge to that specific source rather than writing everything you know about research methods in general. Marks are awarded for linking a named concept directly to details given in the source.
Imagine a novel source describes a researcher who tells participants beforehand, “This study is about whether stress affects memory,” before testing their recall. A strong answer would name demand characteristics specifically, then explain that knowing the aim could lead participants to try harder to remember (or deliberately underperform), which threatens the validity of the results — using the exact detail given in the source as evidence.
A weak answer would only say “the study is biased,” without naming which type of bias applies or linking it to the specific detail in the source. Always name the precise bias, then quote or paraphrase the exact part of the source that shows it.
One research methods task asks you to design an investigation from a scenario. The other gives you a novel source and asks you to analyse and apply your knowledge to it. Both require specific, applied answers — not generic definitions.