How to write the IB Psychology IA

The Psychology IA is the only piece of coursework your Psychology grade is marked on internally — worth 25% of your final grade at SL and 20% at HL. Most students lose marks not because they cannot run an experiment, but because they choose a study that is impossible to replicate safely, never operationalise their variables, or stop at a table of averages without ever running a statistical test. This guide takes you through the whole thing: what the IA is, how it is marked, exactly how to write each part, and what separates a top-band experimental study from an average one.

The IB Psychology IA at a glance

The Psychology IA is an experimental study that partially replicates a published study. You take a piece of established psychological research, pull out one small, testable relationship from it, and rebuild that relationship as a simple experiment you can run yourself. The whole report is about 2,200 words and is marked out of 22 across four criteria. Because it is a replication, the original study does almost all of the theoretical heavy lifting for you — your job is to design the experiment cleanly, run it ethically, analyse the numbers properly, and reflect honestly on what went right and wrong. The word "partially" matters: you are not expected to reproduce the entire original study, only a manageable slice of it.

How the Psychology IA is marked: the four criteria

Every mark you earn comes from one of these four criteria. The most reliable way to write the IA is to treat each criterion as a separate checklist and make sure nothing on it is missing:

How to write a Psychology IA, step by step

1. Choose a simple, ethical study to replicate. Pick a published study with a clean experimental design you can rebuild with classmates as participants — no stress, no deception, nothing that needs special equipment or vulnerable groups.
2. Operationalise your IV and DV, and write the hypothesis. Turn the abstract idea into something you can manipulate and measure exactly, then state a research hypothesis and a null hypothesis that flow from the original study.
3. Design ethically. Plan informed consent, the right to withdraw, anonymity and a debrief, and remove anything that could cause harm or distress.
4. Sample your participants. Choose and justify a sampling method, describe who took part, and explain how they were allocated to conditions.
5. Run the experiment. Carry out the procedure under standardised conditions, holding your controlled variables constant across both conditions.
6. Calculate descriptive and inferential statistics. Report a measure of central tendency and one of dispersion, then run an inferential test that matches your design (independent/repeated measures) and your data.
7. Make a decision. Quote the test statistic and significance level, and state clearly whether you reject or retain the null hypothesis.
8. Evaluate against the original study. Compare your result to the study you replicated, weigh your limitations by their impact, and propose targeted, realistic improvements.

Psychology IA structure: what goes in each section

There is no rigid template, but the structure that maps most cleanly onto the four criteria is:

• Introduction — the aim, the published study you are partially replicating, the relevant background theory, your operationalised IV and DV, and your research and null hypotheses.
• Exploration — your experimental design and why it is appropriate, the sampling method and participants, controlled variables, and the ethical considerations.
• Procedure — a standardised, reproducible account of exactly what participants did, with any materials referenced in an appendix.
• Analysis — descriptive statistics in a clear table and graph, the choice and justification of your inferential test, the calculation, and the decision about the null hypothesis.
• Evaluation — what your result means in relation to the original study, the limitations weighed by impact, and specific improvements.
• References & appendices — a consistent citation style, plus consent forms, briefing and debriefing scripts, standardised instructions and raw data.

What a strong vs weak Psychology IA looks like

The quickest way to raise your marks is to see the same work done two ways. Here are three places where strong and weak IAs diverge.

The hypothesis

The statistics

The evaluation

Common mistakes that cost marks

• No background study. An IA that is not built on a published study to replicate cannot satisfy the Introduction criterion.
• Vague variables. If your IV and DV are not operationalised into something you can manipulate and measure, every later criterion suffers.
• An unethical or messy design. Stress, deception or uncontrolled conditions cap the Exploration marks — keep it ethical and tightly controlled.
• Descriptive statistics only. Stopping at means and a bar chart, with no inferential test, is the single most common way to lose Analysis marks.
• The wrong test. An inferential test that does not match your design or data type undermines your decision.
• Generic limitations. "The sample was small" without weighing its impact, and without linking back to the original study, weakens the Evaluation.
• Drifting far over 2,200 words. The report is meant to be concise — pad it and the analysis gets buried.

Psychology IA — frequently asked questions

Guidance written by experienced IB examiners and aligned to the current Psychology guide. Not affiliated with or endorsed by the International Baccalaureate Organization.