IB® · HL/SL
IB® Psychology HL/SL
The six concepts, three approaches, four contexts, HL extensions, research methods, and the research-proposal IA for the syllabus first assessed in 2027.
Start Unit 1 free. Six Concepts is open to everyone, no account needed. Other topics are locked.
Six Concepts
THE BIG PICTURE. The six concepts are the organising lenses of the 2027 IB Psychology course: bias, causality, change, measurement, perspective, responsibility. They are not separate topics but frameworks for analysis: every essay, SAQ, and IA proposal benefits from explicit concept use. Concept-based extended response (Paper 1 Section C) is the highest-mark question.
BIAS
Systematic deviation from objectivity. Appears in:
- Cognitive biases: confirmation, anchoring, availability, hindsight, in-group favouritism.
- Research bias: sampling bias, demand characteristics, experimenter effects, publication bias.
- Cultural bias: Western WEIRD samples (Henrich 2010); ethnocentric assumptions.
- Diagnostic bias: gender, racial bias in diagnosis.
Application example: in memory research, schema-based bias distorts recall (Bartlett, Loftus). In eyewitness testimony, leading questions exploit memory biases. In diagnosis, clinicians may be biased by patient demographics.
CASE STUDY: THE REPRODUCIBILITY PROJECT (OPEN SCIENCE COLLABORATION, 2015)
Aim. To estimate how often published findings in psychology can be reproduced when the study is run again.
Method. A large international team repeated 100 experimental and correlational studies published in 2008 in three leading psychology journals. They used high-powered designs, original materials where available, and contact with the original authors.
Findings. 97% of the original studies had reported statistically significant results, but only 36% of the replications did. On average, the replication effects were about half the size of the original effects.
Evaluation.
- Strength: large, planned in advance and fully transparent, so the result is itself open to checking.
- Limitation: each study was replicated only once, and some critics (e.g., Gilbert and colleagues, 2016) argued that differences between the original and replication samples or procedures explain part of the drop.
- A failed replication does not prove the original finding false; it lowers our confidence in it.
Link to the concepts.
- Bias: publication bias (journals favour significant results) and flexible analysis can fill the literature with false positives.
- Measurement: statistical significance is not the same as a large or reliable effect; type I errors are more common with small samples.
- Responsibility: researchers should make the uncertainty in their findings clear to the public.
CAUSALITY
The relationship between cause and effect. Different research methods support different causal claims:
- True experiments: random assignment + IV manipulation → strongest causal claims.
- Correlational studies: only show association, not causation.
- Quasi-experiments / natural experiments: limited causal claims due to no random assignment.
- Case studies, qualitative: generate hypotheses, not causal conclusions.
Common causal challenges:
- Third-variable problem (e.g., ice cream and drowning: both caused by hot weather).
- Bidirectional ambiguity (does stress cause depression or depression cause stress?).
- Selection effects.
- Reverse causation.
Application: in stress and illness research (Cohen 1991), the experimental design (controlled exposure to viruses) supports causation; in observational studies of stress, correlation only.
Causality depends on the method Only a true experiment, with a manipulated IV and random allocation, can support a cause-and-effect claim on its own. Quasi-experiments and correlational studies show differences and relationships; qualitative and case studies explain experience and generate hypotheses to test.
CHANGE
How psychological phenomena vary across:
- Time: developmental change (Piaget); change with intervention (CBT).
- Situations: behaviour varies by context (situationism).
- Cultures: psychological constructs differ across cultural contexts.
Cross-sectional (different ages at same time) vs longitudinal (same people over time) designs.
Application: neuroplasticity (Maguire taxi drivers) shows physical brain change with experience. Stages of Change Model (Prochaska) tracks behaviour-change progression. Social identity can shift with intergroup contact.
Designs that track change (a related term for this concept):
| Design | How it works | Strength | Limitation |
|---|---|---|---|
| Longitudinal | The same people are measured repeatedly over months or years | Shows change within individuals and the order of events | Slow, costly; participants drop out (attrition) |
| Cross-sectional | Different age groups are measured once, at the same time | Quick and cheap | Differences may reflect generation (cohort), not development |
| Repeated measures | The same participants do every condition of an experiment | Controls participant variables | Order effects (practice, fatigue) need counterbalancing |
| Prospective vs retrospective | Measure the cause first and follow forward, or ask about the past | Prospective data avoid memory distortion | Retrospective reports are open to recall bias |
MEASUREMENT
How psychological constructs are operationalised and quantified.
Key issues:
- Operationalisation: defining "intelligence" or "happiness" in measurable terms.
- Reliability: consistency of measurement.
- Validity: does the measure capture the construct?
- Quantitative vs qualitative measurement.
Common psychometric tools:
- Self-report scales (Likert).
- Reaction-time measures.
- Physiological measures (cortisol, heart rate, fMRI).
- Observation rating systems.
- Standardised tests (IQ, depression inventories).
Application: measuring "depression": Beck Depression Inventory (BDI) self-report; clinical interview (DSM criteria); biomarkers (cortisol, HPA axis dysregulation). Each measure has reliability and validity strengths/limits.
PERSPECTIVE
Different viewpoints shape understanding:
- Theoretical perspectives: biological vs cognitive vs sociocultural explanations.
- Cultural perspectives: etic (outsider, comparative) vs emic (insider, within-culture).
- Methodological perspectives: quantitative vs qualitative.
- Stakeholder perspectives: researcher vs participant vs public vs policy.
- Indigenous perspectives: psychology grounded in Indigenous knowledge systems and worldviews.
Application: abnormality is defined differently across cultures (culture-bound syndromes); memory is approached differently in Western individualistic vs Asian collectivist cultures (Markus & Kitayama).
RESPONSIBILITY
Ethical accountability in research and application:
- Researcher responsibility: ethical guidelines (consent, debriefing, harm avoidance, IRB review).
- Practitioner responsibility: duty of care, evidence-based practice.
- Societal responsibility: using psychological knowledge for good (avoiding misuse, e.g., propaganda, manipulation).
- Participant safeguards: vulnerable populations, animals.
- Application of findings: what should we do with knowledge of stereotypes, bias, manipulation?
Application: Milgram's obedience study (1963) raised lasting responsibility questions: caused distress; informed consent and right to withdraw violated. Drove modern ethics codes (IRBs, BPS guidelines).
PRACTICE: WHICH CONCEPT IS AT ISSUE?
| Scenario | Main concept | Why |
|---|---|---|
| A researcher who knows which participants took the real drug rates their mood | Bias (researcher bias) | Expectations can colour ratings; a double-blind design removes this |
| Heavy phone use correlates with low mood in teenagers | Causality (bidirectional ambiguity) | Low mood may lead to more phone use, not only the reverse |
| "Happiness" is operationalized as the number of smiles in ten minutes | Measurement (validity) | Smiling may not capture the construct of happiness |
| Anxiety is rated before therapy, then at 6 and 12 months | Change (longitudinal design) | Tracks the same people over time |
| A Western attachment test is used unchanged in a very different culture | Perspective (imposed etic) | The categories may not mean the same thing there |
| After a partial deception, participants are debriefed and offered the chance to withdraw their data | Responsibility (ethics) | Protects participants' rights and trust |
INTEGRATING CONCEPTS
Strong essays apply multiple concepts to a single phenomenon. Example: stress and illness:
- Bias: demand characteristics in self-report stress measures.
- Causality: experimental design (Cohen 1991) supports causation; observational does not.
- Change: stress reactions develop over time (GAS); CBT changes them.
- Measurement: cortisol vs self-report stress measures differ.
- Perspective: biological (HPA axis) vs cognitive (Lazarus appraisal) vs sociocultural (cultural stressors).
- Responsibility: ethical considerations in inducing stress in lab studies.
How concepts are assessed. Concept-based questions appear in Paper 1 Section C and Paper 2 Section B. The related terms listed under each concept in the subject guide are guidance only: they will not be used to set these questions, and other relevant terms are accepted as long as the link to the concept is explained and justified. There is no single correct way to apply a concept, so the skill being rewarded is the quality of the link, not the choice of term.
WORKED EXAMPLE: PLANNING A PAPER 1 SECTION C RESPONSE (15 MARKS)
Prompt (written for this guide): To what extent does measurement limit our understanding of stress and health?
Plan.
- Introduction: define measurement (operationalizing a construct so it can be recorded reliably and validly). Thesis: measurement choices limit how precisely and how causally we can talk about stress, but triangulating several measures reduces the problem.
- Paragraph 1, self-report: stress scales and life-event checklists are quick and capture the person's own appraisal, but they depend on honest, accurate recall and are open to social desirability. Link: what is measured is reported stress, not stress itself.
- Paragraph 2, physiological measures: cortisol is objective, but it changes across the day and reflects arousal, not whether the person feels threatened. Link: an objective number can still be an indirect measure of the construct.
- Paragraph 3, combining measures: Cohen et al. (1991) paired a questionnaire stress index with laboratory evidence of infection after controlled virus exposure. Triangulation made the stress-illness link more credible, but stress was measured, not manipulated, so the causal claim stays limited.
- Counterargument: qualitative interviews show what stress means to people, which numbers miss; seen this way, measurement is a choice of lens as much as a limitation.
- Conclusion: measurement limits our understanding to a large extent when a single measure is used, and to a smaller extent when methods are triangulated. State the judgment clearly and make it follow from the paragraphs.
Why the plan works. Each paragraph ties a specific piece of content back to measurement, so the concept runs through the whole response, and the conclusion answers "to what extent" with a reasoned position. No sample sizes are needed: the top markband rewards explained links and critical analysis, not recall of study details.
EXAM CONNECTIONS. Paper 1 Section C explicitly demands concept-based analysis. Practise applying each concept to multiple content areas. Don't just name the concept: show how it shapes interpretation of evidence.
Key Terms
Bias (concept)
Systematic deviation from objectivity. Includes cognitive biases (confirmation, anchoring), research biases (sampling, demand characteristics), and cultural bias (WEIRD samples).
Causality (concept)
Cause-effect relationships. Strongest causal claims require true experiments (random assignment + IV manipulation). Correlational designs cannot establish causation.
Change (concept)
Variation across time, situations, or interventions. Studied via longitudinal, cross-sectional, or experimental designs. Includes neuroplasticity, developmental change, and intervention effects.
Measurement (concept)
Operationalising and quantifying psychological constructs. Includes reliability, validity, and choice of tools (self-report, behavioural, physiological, observational).
Perspective (concept)
Viewpoints shaping interpretation: theoretical (bio/cog/sociocultural), methodological (quan/qual), cultural (etic/emic), Indigenous, stakeholder.
Responsibility (concept)
Ethical accountability: researcher (consent, harm avoidance), practitioner (duty of care), societal (avoiding misuse). Drives ethics codes and IRB review.
Etic vs Emic Perspectives
Etic: outsider, cross-cultural comparison. Emic: insider, within-culture understanding. Both used in 2027 sociocultural research; emic increasingly emphasised, including Indigenous psychology.
WEIRD Samples
Western, Educated, Industrialised, Rich, Democratic: Henrich et al. (2010) noted ~95% of psychology research uses such samples, threatening generalisability and introducing cultural bias.
Exam Tips
- Apply MULTIPLE concepts to a single phenomenon for top-band Paper 1 Section C marks.
- Don't just name a concept: explain HOW it shapes interpretation of evidence.
- Pair concepts with content: bias + memory studies; causality + experimental design; change + neuroplasticity.
- Etic and emic should both appear in cross-cultural sociocultural responses.
- For "responsibility", link to specific ethical issues in named studies (Milgram, Stanford Prison, Tuskegee).
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