Every Primary examination report publishes one figure per subject: the cohort's mean percentage of correct answers in anatomy, pathology, physiology and pharmacology. Nineteen sittings of those figures answer two questions candidates ask constantly. Which subject is hardest? And, since the 2022.2 rule change made each subject a separate hurdle, how far below the pack can one subject fall before it fails you on its own?
Scores by subject, every sitting
| Sitting | Anatomy | Pathology | Physiology | Pharmacology | Lowest | Highest | Spread |
|---|---|---|---|---|---|---|---|
| 2017.1 | 70.3% | 62.8% | 61.4% | 66.2% | Physiology | Anatomy | 8.9 |
| 2017.2 | 68.0% | 65.8% | 63.5% | 68.9% | Physiology | Pharmacology | 5.4 |
| 2018.1 | 73.0% | 71.6% | 66.1% | 71.4% | Physiology | Anatomy | 6.9 |
| 2018.2 | 72.8% | 71.0% | 71.0% | 70.0% | Pharmacology | Anatomy | 2.8 |
| 2019.1 | 71.8% | 71.6% | 71.1% | 71.1% | Physiology | Anatomy | 0.7 |
| 2019.2 | 74.9% | 70.1% | 69.1% | 76.2% | Physiology | Pharmacology | 7.1 |
| 2020.1 | 68.0% | 70.0% | 68.0% | 72.0% | Anatomy | Pharmacology | 4.0 |
| 2020.2 | 74.7% | 73.3% | 73.1% | 75.0% | Physiology | Pharmacology | 1.9 |
| 2021.1 | 71.1% | 74.2% | 72.0% | 73.5% | Anatomy | Pathology | 3.1 |
| 2021.2 | 72.8% | 69.4% | 70.2% | 76.5% | Pathology | Pharmacology | 7.1 |
| 2022.1 | 72.0% | 71.2% | 66.9% | 73.8% | Physiology | Pharmacology | 6.9 |
| 2022.2 | 67.2% | 72.4% | 70.3% | 73.7% | Anatomy | Pharmacology | 6.5 |
| 2023.1 | 71.6% | 70.8% | 70.4% | 73.7% | Physiology | Pharmacology | 3.3 |
| 2023.2 | 68.3% | 67.3% | 73.9% | 71.1% | Pathology | Physiology | 6.6 |
| 2024.1 | 71.1% | 69.8% | 71.6% | 70.8% | Pathology | Physiology | 1.8 |
| 2024.2 | 68.7% | 67.3% | 70.5% | 69.7% | Pathology | Physiology | 3.2 |
| 2025.1 | 70.5% | 68.4% | 66.4% | 72.6% | Physiology | Pharmacology | 6.2 |
| 2025.2 | 69.7% | 67.9% | 65.5% | 66.4% | Physiology | Anatomy | 4.2 |
| 2026.1 | 73.8% | 73.9% | 69.8% | 76.0% | Physiology | Pharmacology | 6.2 |
| Average, 19 sittings | 71.1% | 69.9% | 69.0% | 72.0% | Physiology (11 of 19) | Pharmacology (10 of 19) |
Physiology is the hardest subject, but not by much
Averaged over nineteen sittings, candidates scored 72.0% in pharmacology, 71.1% in anatomy, 69.9% in pathology and 69.0% in physiology. Physiology was the lowest of the four in 11 sittings and pharmacology the highest in 10. That is a consistent pattern, and it fits what most candidates would guess: pharmacology rewards memorised facts that MCQs test well; physiology asks for applied reasoning about systems, which is harder to do reliably at one minute a question.
But the size of the effect matters more than the direction. The gap between the best and worst subject within a single sitting has ranged from 0.7 points (2019.1) to 8.9 points (2017.1), and has not exceeded 7.1 points in any sitting since 2018. In three recent sittings (2023.2, 2024.1 and 2024.2) physiology was the highest-scoring subject. Anatomy, the subject candidates most often describe as the one they fear, was the lowest-scoring subject in only three sittings and the highest in five.
The honest conclusion is that the four subjects are close to equally hard for the cohort as a whole. What differs is the individual candidate. A registrar from a surgical background will find anatomy easier and physiology harder; a candidate with a pharmacology degree will find the reverse. The cohort averages tell you the paper is balanced. Your own practice scores by subject tell you where your gap is, and since 2022.2 that gap is what fails people.
The subject minimum standard
From the 2022.2 sitting, the reports state the pass criteria in full. To pass the Primary Written Examination a candidate must achieve:
- an overall score at or above the examination cut score, as determined by standard setting, plus one standard error of measurement; and
- a minimum standard in all subject areas, defined as scoring at or above the subject cut score minus one standard error of measurement.
Only one report, 2022.2, published what the subject floors actually were. They are worth studying because they show how the rule bites.
| Subject (2022.2) | Cohort mean | Minimum standard required | Gap |
|---|---|---|---|
| Anatomy | 67.2% | 62.3% | 4.9 points |
| Pathology | 72.4% | 52.8% | 19.6 points |
| Physiology | 70.3% | 62.6% | 7.7 points |
| Pharmacology | 73.7% | 63.2% | 10.5 points |
| Whole paper | 70.9% | 65.9% (overall pass mark) | 5.0 points |
Three things follow from that table.
- The floor is well below the overall pass mark. In 2022.2 the overall cut was 66% of marks; the subject floors were 53% to 63%. The rule is not asking you to pass each subject. It is asking you not to collapse in one.
- The floors differ by subject. Pathology's floor was ten points lower than the other three, presumably because the standard setters judged the pathology questions harder that sitting. The floor moves with each paper, so there is no fixed number to aim for. The cohort mean in each subject sat 5 to 20 points above its floor.
- A uniformly average candidate is safe; an unbalanced one is not. A candidate at 70% overall with 70% in each subject clears everything. A candidate at 70% overall who reached it with 78% in pharmacology and anatomy, 66% in pathology and 58% in physiology would have failed 2022.2 on the physiology floor of 62.6%, with a pass-level total score.
The reports do not say how many candidates fail on a subject floor while passing overall. What they do show is the aggregate effect of the new criteria: the pass rate fell from 92% in 2022.1 to 74% in 2022.2 with an unchanged cohort mean, and has averaged 70% since against 86% before. Part of that is the overall cut moving up about four points; part of it, of unknown size, is the subject floor. The pass-rate analysis covers the overall effect in detail.
What this means for how you study
- Track your practice scores by subject, not just overall. The overall score can hide the subject that will fail you. Any subject running more than eight to ten points below your others is the priority, whatever it is.
- Do not drop a subject to concentrate on the others. Under the old criteria a candidate could compensate for weak pathology with strong pharmacology. Under the current criteria they cannot. The subject you like least needs to reach the floor on its own.
- Expect physiology to need the most repetition. Not because the questions are harder in isolation, but because the cohort data show it is the subject most often at the bottom, and it is the one where reasoning under time pressure rather than recall decides the answer. Practise physiology questions to a one-minute clock.
- Treat the subject matrix as the syllabus. The reports state that questions are selected from the item bank in accordance with the subject matrices published by ACEM. Study time that maps to the matrix weights maps to the marks.
- Aim for balance above 70%. Since 2022.2 the overall pass mark has been 63.6% to 66.0% and the cohort average 67% to 74%. A candidate at 70% or better in all four subjects has been above both the overall line and every published floor in every sitting on record.
The paper itself
- 360 multiple-choice questions in two three-hour papers on one day, one minute per question. Extended matching questions were dropped from 2021.2.
- Questions are removed after each sitting following psychometric review: 1 to 9 per sitting before 2022.2, 4 to 16 since, so the paper is now marked out of 344 to 356.
- Two sittings a year, February and August, with results about two weeks later. Pass rates do not differ between them.
- The cohort's spread is wide. In every sitting the lowest score has been 38% to 50% of marks and the highest 86% to 92%.
Sources and method
Subject means are the "mean score (percentage of correct questions)" figures published in Appendix 1 and the historical Appendix 3 of the ACEM Primary Written Examination Reports 2019.1 to 2026.1, which together cover 2017.1 onwards. The per-subject minimum standards are from the 2022.2 report, the only one to publish them. The reports do not give per-subject question counts, standard deviations, or the number of candidates failing on a subject floor. ACEMCQ is independent of ACEM and this analysis is not endorsed by the College.
Frequently asked questions
Which subject is hardest in the ACEM Primary exam?
Physiology. It was the lowest-scoring subject in 11 of 19 sittings from 2017 to 2026, with a mean of 69.0% against 72.0% for pharmacology, 71.1% for anatomy and 69.9% for pathology. The differences are small, usually within three to seven points in any one sitting.
What is the subject minimum standard in the ACEM Primary exam?
Since 2022.2, passing requires an overall score at or above the examination cut score plus one standard error of measurement, and a score in each of the four subjects at or above that subject’s cut score minus one standard error of measurement. In the one sitting where the subject floors were published (2022.2) they were 62% for anatomy, 53% for pathology, 63% for physiology and 63% for pharmacology.
Can you fail the ACEM Primary on one subject?
Yes. A candidate above the overall pass mark who falls below the minimum standard in any one subject fails. The reports do not say how many candidates this affects, but the pass rate fell from 92% to 74% in the sitting the rule was introduced, while the cohort average was unchanged.
How many questions per subject are in the ACEM Primary written exam?
The paper is 360 MCQs across two three-hour papers, drawn from the item bank according to the subject matrices published on the ACEM website. The examination reports do not publish the per-subject question counts for each sitting.