IB Diploma Programme Psychology SL (first assessment 2021; current guide). This topic covers the CORE's first two approaches in full: the biological approach (the brain and behaviour, hormones and behaviour, genetics and behaviour) and the cognitive approach (cognitive processes, the reliability of cognitive processes, emotion and cognition). Every claim below travels with a named study — in IB psychology an unaccompanied theory earns nothing. The worked numbers are the published findings of the classic studies, rounded where noted.

Must-know for the core approaches:

The biological approach 生物取向 explains behaviour by physiological processes: brain structures, brain chemistry and genetics — thought, feeling and action are what the body does. Localisation of function 功能定位 holds that specific brain areas do specific jobs; the case of Phineas Gage (iron rod through the frontal lobe, 1848; personality changed, faculties otherwise intact) and patient H.M. (surgery removed the hippocampi, 1953; new long-term memories never formed, procedural memory intact) are the classic case studies — rich in detail, and exactly as limited as any $n = 1$. Neuroplasticity 神经可塑性 is the brain's remodelling with use: Maguire et al. (2000) found London taxi drivers' posterior hippocampi larger than controls', growing with years of navigation — but taxi driving also differs in a dozen other ways, so the fMRI correlation is not causation. TECHNIQUES: fMRI shows activation (spatial, indirect, correlational); EEG/ERP shows timing (temporal, but the skull smears the source); MRI shows structure; post-mortem examination confirms anatomy after death.

Hormones 激素 are chemical messengers: chronic CORTISOL elevation under stress impairs hippocampal memory; TESTOSTERONE relates to aggression (Dabbs et al. found higher salivary testosterone among violent offenders than non-violent — a correlation with many confounds); OXYTOCIN rises with trust and bonding (Kosfeld et al., 2005: nasal oxytocin raised trust-game transfers — a small, induced, laboratory effect). Genetics and behaviour: genes set ranges, not destinies. Twin studies compare identical (MZ) with fraternal (DZ) twins — schizophrenia concordance runs near 50% for MZ against roughly 15–20% for DZ (Gottesman): substantial heritability, and equally clear non-heritability, since identical genes do not guarantee the outcome. The gene–environment interaction 基因环境交互作用 is Caspi et al. (2003): among people suffering severe life stress, depression followed for about 33% of those carrying two short 5-HTT alleles against about 17% of those with two long alleles — the gene matters only in its environment.

The cognitive approach 认知取向 treats the mind as an information processor — input, encoding, storage, retrieval, output — studied rigorously since the 1950s "cognitive revolution". MEMORY MODELS: the MULTI-STORE model (Atkinson–Shiffrin) separates sensory, short-term and long-term stores; its evidence includes the serial position curve (primacy from the long-term store, recency from the short-term store, and recency vanishes after a short filled delay, Glanzer–Cunitz 1966). Working memory 工作记忆 (Baddeley–Hitch) replaces a single short-term store with an executive plus slave systems, predicting the word-length effect (fewer long words recalled: articulatory rehearsal is time-limited). Schema theory: knowledge is organised in schemas 图式 that guide encoding and retrieval; Bartlett's "War of the Ghosts" (1932) showed participants reshaping an unfamiliar story toward their own cultural schemas on every retelling — memory is reconstructive 重构记忆, not a videotape.

RELIABILITY: leading questions 引导性问题 distort recall — Loftus and Palmer (1974): watching the same crash, participants estimated 40.8 mph for "smashed" against 34.0 mph for "hit", and a week later more of the "smashed" group "remembered" broken glass that never was. But Yuille and Cutshall (1986) found real witnesses of a shooting highly accurate months later — high stress, real event, no leading interviewer: reliability depends on conditions, not a fixed human flaw. BIASES: the availability heuristic judges frequency by ease of recall (Tversky–Kahneman), so vivid events feel common. EMOTION AND COGNITION: Brown–Kulik's FLASHBULB memories feel photographic — but Neisser and Harsch (1992) found Challenger-shuttle memories changed substantially over 32 months while confidence stayed high: vivid is not accurate. LeDoux's two routes — a fast amygdala path and a slower cortical path, explaining emotional responses that outrun conscious appraisal.

• Localisation with Gage and H.M.; neuroplasticity with Maguire; the four techniques and what each can and cannot show (biological).
• Cortisol, testosterone (Dabbs) and oxytocin (Kosfeld) as correlational messengers (biological).
• Twin studies (MZ/DZ concordance) and Caspi's 5-HTT interaction; genes as ranges, not destiny (biological).
• Multi-store with the serial position curve; working memory with the word-length effect; schema theory with Bartlett (cognitive).
• Leading questions with Loftus–Palmer's 40.8/34.0 mph and the Yuille–Cutshall counterpoint; availability bias (cognitive).
• Flashbulb memory (Brown–Kulik, Neisser–Harsch) and LeDoux's two routes (cognitive).

Boundary notes: Paper 1 Section A (short-answer, [9]) rewards ONE accurate study per approach named precisely — researcher, method, finding; Section B essays ([22]) require evaluation — strengths, limitations and the assumption each study rests on. All study findings cited are the published classic results; where they are rounded, the direction and gap are as reported.

IB Diploma Programme Psychology SL (first assessment 2021; current guide). This topic covers the CORE's third approach in full — the sociocultural approach (the individual and the group, cultural origins of behaviour and cognition, cultural influences on attitudes and identities) — and then the OPTIONS menu: abnormal psychology, developmental psychology, health psychology and the psychology of human relationships (SL schools teach ONE option; this handout equips all four so any school's choice is covered). Every claim travels with a named study, and the classic findings' numbers are as published.

Must-know for the sociocultural core and options:

Social identity theory 社会认同理论 (Tajfel and Turner) explains intergroup behaviour in three steps — SOCIAL CATEGORISATION (sorting self and others into groups), SOCIAL IDENTIFICATION (adopting the in-group's identity) and SOCIAL COMPARISON (favouring the in-group to build self-esteem). TAJFEL'S MINIMAL GROUPS (1971): Bristol schoolboys allocated by a coin-flip-like criterion (dot estimation) still awarded more points to their own anonymous group — mere categorisation produces in-group favouritism. Stereotypes are schemas about groups — quick but resistant to contrary evidence; STEELE and ARONSON (1995) showed stereotype threat 刻板印象威胁: Black students performed worse than White students only when a test was framed as diagnostic of ability, showing the stereotype doing measurable work.

SOCIAL INFLUENCE. Conformity 从众 — Asch (1951): judging line lengths against a unanimous wrong majority, about 75% of participants conformed at least once and roughly a third of critical trials went with the majority; one dissenting ally collapses conformity. Obedience 服从 — Milgram (1963): 26 of 40 participants (65%) administered the full 450 V in a staged learning experiment — ordinary people follow destructive orders under graduated authority and proximity. The two differ in the source of pressure (peers' unanimity versus authority's commands), and both are culture-sensitive: Bond and Smith's meta-analysis found conformity lower in individualist cultures.

CULTURE. Cultural dimensions 文化维度 (Hofstede) — individualism versus collectivism, power distance, uncertainty avoidance, masculinity (later long-term orientation) — describe national value systems from workplace surveys; the trap is the ecological fallacy: describing cultures, never individuals. Enculturation 文化濡化 is learning one's own culture's norms; conformity studies double as evidence that norms are culture-bound (as the drift of Asch's effect across decades and countries shows). Acculturation 文化适应 follows when cultures meet: Berry's four strategies — ASSIMILATION (adopt, abandon), INTEGRATION (adopt and keep), SEPARATION (keep, avoid), MARGINALISATION (neither) — with INTEGRATION generally the healthiest profile.

Bicultural identity: Benet-Martínez shows people can hold two cultural frames with varying integration — biculturals switch interpretive frames with cultural cues (frame switching), and higher identity integration predicts wellbeing. Acculturation research links STRATEGY to OUTCOME: integration associates with better mental health, marginalisation with the worst (Berry's comparative studies) — evidence that identity negotiation, not contact alone, carries the stress.

THE OPTIONS (SL schools teach one; each below is a complete mini-kit of explanations, one anchor study and application). ABNORMAL PSYCHOLOGY — diagnosis 诊断: DSM/ICD categories rest on reliability and validity; ROSENHAN (1973) sent 8 pseudopatients to 12 hospitals complaining of one symptom; all but one were admitted with schizophrenia, kept 7–52 days, and were discharged "in remission" — the label shaped how staff read ordinary note-taking, while real patients often saw through it. Etiology of major depression: biological (genetic liability, monoamine activity), cognitive (Beck's negative triad; learned helplessness) and sociocultural (life events, isolation) — multi-factorial by default. Treatment: CBT restructures the triad with effects comparable to SSRIs and lower relapse after withdrawal; combined treatment leads for severe cases. DEVELOPMENTAL PSYCHOLOGY — brain development: Romanian orphanage research (Rutter's ERA) shows severe early deprivation impairing later cognition and attachment, with earlier adoption buying better catch-up; cognitive development: false-belief understanding appears around age four (Wimmer–Perner's Sally–Anne task), mapping Piagetian stages onto theory of mind; identity development: Erikson's stage crisis and Marcia's identity statuses (achievement, moratorium, foreclosure, diffusion); developing as a learner: metacognition and attributional style, not "learning styles", move performance. HEALTH PSYCHOLOGY — determinants: the socioeconomic gradient (Whitehall II: lower employment grade, higher mortality, independent of access); stress: chronic cortisol impairs immune function — Kiecolt-Glaser's caregivers' wounds healed markedly slower than controls'; health promotion: the health-belief model (perceived susceptibility, severity, benefits, barriers, cues) predicts screening uptake where fear alone does not. PSYCHOLOGY OF HUMAN RELATIONSHIPS — personal relationships: formation follows proximity, similarity and perceived attractiveness — in Walster's computer-dance study the partner's rated attractiveness, not one's own, predicted liking; group dynamics: SHERIF's Robbers Cave showed intergroup hostility built by competition and reversed by superordinate goals 超级目标; social responsibility: bystanderism 旁观者效应 — Darley and Latané's seizure study: 85% helped alone against 31% with four others believed present (smoke version: 75% against 10%) — diffusion of responsibility 责任扩散, not apathy.

• Social identity theory's three processes with Tajfel's minimal groups; stereotypes and Steele–Aronson's stereotype threat (sociocultural).
• Asch's ≈75%/≈37% with the ally effect; Milgram's 26/40 = 65% with the graduated-commitment mechanism; conformity versus obedience (sociocultural).
• Abnormal: Rosenhan's 8/12/7–52 days; depression's three-level etiology; CBT versus SSRIs.
• Developmental: Rutter's orphans; Sally–Anne at ~4; Marcia's statuses; metacognition as the learner lever.
• Health: the Whitehall II gradient; Kiecolt-Glaser's slow-healing caregivers; the health-belief model's five parts.
• Relationships: Walster's attractiveness finding; Sherif's superordinate goals; Darley–Latané 85%/31% and diffusion of responsibility.

Boundary notes: Paper 1 Section A SAQs [9] want one precise study per concept; the option paper's essays [22] demand ERQ evaluation — strengths, limitations, assumptions. All numbers are the published classic results.

IB Diploma Programme Psychology SL (first assessment 2021; current guide). This topic covers the CORE's "approaches to researching behaviour" in full — the quantitative methods (experiments and their designs, correlational studies, descriptive statistics) and the qualitative and mixed toolset (case studies, observations, interviews, questionnaires), with sampling, ethics and the evaluation concepts (generalizability, credibility, bias) — and then the INTERNAL ASSESSMENT, the experimental study and its report. The worked numbers are an original rehearsal experiment whose arithmetic is carried through the page.

Must-know for research methods:

The EXPERIMENT is psychology's causal instrument: manipulate the independent variable 自变量 (IV), control the rest, measure the dependent variable 因变量 (DV). LAB experiments control maximally at the cost of ecological validity; FIELD experiments trade control for realism; NATURAL experiments exploit existing differences the researcher cannot manipulate; QUASI-experiments use pre-existing groups without random allocation. DESIGNS: INDEPENDENT MEASURES (one group per condition — no order effects, but participant variables between groups; random ALLOCATION balances them), REPEATED MEASURES (everyone does both conditions — no participant variables, but order effects, managed by counterbalancing) and MATCHED PAIRS (a compromise costing matching time). Demand characteristics 需求特征 — participants guessing the study's aim — are attacked with standardised instructions, single-blind designs and cover stories that stay within ethics.

SAMPLING: Random sampling 随机抽样 gives everyone an equal chance (representative in principle, hard in practice); OPPORTUNITY sampling takes who is available (cheap, biased toward the accessible); VOLUNTEER (self-selected) samples are cooperative but unrepresentative — the self-selection bias. Sampling chooses WHO you test; ALLOCATION assigns them to conditions — random sampling is not random allocation, and confusing the two is the classic IA error. Descriptive statistics 描述统计: the MEAN uses every score but is dragged by outliers; the MEDIAN resists them; the MODE fits categories. Dispersion: the RANGE is quick but rests on two scores; the STANDARD DEVIATION uses them all. CORRELATION measures association without manipulation — the correlational study 相关研究 gives a coefficient $r$ from $-1$ through 0 to $+1$, and never a direction of cause: sleep and grades correlate; so may the third factor behind both.

Worked example (the rehearsal experiment). Does semantic processing beat acoustic processing for word recall? Repeated-measures design, counterbalanced (AB/BA), 10 participants, standardised word lists. Group means: acoustic 6.0 words, semantic 8.7 words. The mean difference (2.7 words) is DESCRIPTIVE — it says what happened in this sample; variability (one acoustic participant recalled 11, above the semantic median) shows why ranges and SDs travel with means.

CASE STUDIES examine one person or event in depth (H.M., Gage) — richness against generalizability. OBSERVATIONS may be NATURALISTIC or CONTROLLED, OVERT or COVERT, PARTICIPANT or NON-PARTICIPANT; they need BEHAVIOURAL CATEGORIES and inter-rater reliability 评分者间信度 (two observers agreeing, checked on a coefficient). INTERVIEWS run structured (fixed questions, comparable), semi-structured (pursue the interesting answer) or as FOCUS GROUPS (interaction itself is data — and a source of conformity). QUESTIONNAIRES scale cheaply but suffer social-desirability bias and item ambiguity. TRIANGULATION — combining methods, data sources or researchers — is the qualitative answer to single-lens error.

ETHICS (and the IA is marked on it): Informed consent 知情同意, deception only when unavoidable with full DEBRIEF, protection from harm, the RIGHT TO WITHDRAW at any time, CONFIDENTIALITY, and for animals the 3Rs. The evaluation concepts: GENERALIZABILITY (do findings travel beyond this sample and setting?), CREDIBILITY (do the findings reflect the participants' reality — in qualitative work: credibility, transferability, dependability, confirmability?) and BIAS (researcher expectancy, participant reactivity, sampling bias).

The IA (SL and HL) is a SIMPLE EXPERIMENT the student designs, runs and reports on a small sample — original data, ethically conducted. The report's structure mirrors the method. INTRODUCTION: background theory (one or two studies), the rationale, and an operationalised AIM. EXPLORATION: the design (which of the three, and why), variables identified and operationalised, CONTROLS (standardised instructions and materials, counterbalancing, environment), the sampling method and sample with its limits, ETHICS addressed point by point (consent forms in the appendix), and materials. ANALYSIS: descriptive statistics with correctly labelled graphs of the measures of central tendency and dispersion. EVALUATION: strengths, LIMITATIONS tied to the design and sample, and modifications that follow from them. APPENDICES: raw data, sign-up sheets, standardised instructions 标准化指示, consent forms. The marking criterion rewards a study whose design choices are EXPLAINED, not just listed — every choice carries a because.

Worked example (the report's spine). Aim: to investigate the effect of processing level (shallow/acoustic vs deep/semantic) on word recall in a repeated-measures experiment. Design choice: repeated measures removes participant variables; counterbalancing (half do A then B, half B then A) removes order effects. Controls: same word list lengths, same 60-second recall window, written standardised instructions read aloud. Sample: 10 volunteers from one school year (opportunity sampling — limited generalizability, stated). Ethics: informed consent from participants, right to withdraw, no deception, anonymised data. Analysis: means 6.0 vs 8.7 with ranges and a bar chart of means. Evaluation: volunteer bias and single-year sample limit transfer; a replication across year groups and a larger sample are the named modifications.

• The four experiment types with their control–realism trade-offs; the three designs with order effects and counterbalancing (quantitative).
• IV and DV operationalised; demand characteristics and the standardised countermeasures (quantitative).
• Random, opportunity and volunteer sampling with allocation distinguished from sampling (quantitative).
• Mean, median, mode, range, SD — what each is good and bad at; correlation's $r$ and its no-causality rule (quantitative).
• Case studies, observations with inter-rater reliability, interviews and focus groups, questionnaires, triangulation (qualitative).
• The six ethical principles and the 3Rs; generalizability, credibility and the bias family (ethics; evaluation).
• The IA report's five sections (aim, design, controls, ethics, statistics, evaluation), marked on explained choices and correct descriptive statistics; all worked numbers are original to the rehearsal experiment.