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IB DP Psychology — Concepts | SL & HL | Paper 1
🎯 Learning Intentions By the end of this note, you will be able to:
- Define sampling bias, confirmation bias, and publication bias using IB-aligned terminology.
- Explain how each type of bias threatens the validity and generalisability of psychological research.
- Describe the conditions under which each bias is most likely to occur in psychological research.
- Evaluate research evidence related to bias using supporting and opposing studies in ACAS format.
- Apply concepts of bias to a real-world case study from a psychological research perspective.
- Discuss the extent to which bias undermines the conclusions drawn from psychological research.
- Analyse the role of bias using relevant concept areas: Bias, Causality, Measurement, Perspective, and Responsibility.
Introduction & Context
Imagine a researcher wants to understand how much stress university students experience. She surveys 200 students — all from her own institution, all psychology majors, and all volunteers who responded to a poster on the department noticeboard. The study produces clear, confident results. But should we trust them? The students who chose to participate may be especially interested in mental health. Psychology students may think about stress differently from engineering or arts students. And the single university may not represent the diversity of student life globally.
This is not an unusual situation in psychology — it is, in fact, the norm. Research in psychology is conducted by human beings, using human participants, interpreted by human minds. At every stage of this process, systematic errors can creep in that distort what we find, what we believe, and what gets published. These systematic errors are called biases , and understanding them is essential not just for evaluating research, but for understanding why the scientific record in psychology is sometimes less reliable than it appears.
🔍 Analogy — The Bent Mirror Think of psychological research as a mirror that reflects human behaviour. Ideally, the mirror should be perfectly flat — showing reality as it is. But bias bends the mirror. Sampling bias bends it by only reflecting certain kinds of people. Confirmation bias bends it by making the researcher see what they expect to see. Publication bias bends it by only showing the reflections that look interesting or positive, hiding the rest. The result is a distorted image that we mistake for truth.
Core Concepts
Before a researcher can study human behaviour, they must decide who to study. This decision — seemingly practical — has profound consequences for what conclusions can be drawn. If the people selected for a study do not represent the broader population the researcher wants to understand, then any findings from that study may only apply to the narrow group who participated. The problem is not just that the sample is small; it is that the sample is systematically different from the population in ways that matter.
📖 Key Definition — Sampling Bias Sampling bias occurs when the sample used in a study is not representative of the population the researcher intends to generalise to, because certain groups are systematically over-represented or under-represented. This threatens the external validity of the research — the degree to which findings can be applied beyond the specific sample studied.
The most frequently cited example of sampling bias in psychology is the over-reliance on WEIRD participants — those from Western, Educated, Industrialised, Rich, and Democratic societies. Henrich, Heine, and Norenzayan (2010)