The Knowledge You Need

The questions are designed so that you don't need knowledge beyond A-level. But that means the whole specification, understood well enough to reason from. There is also a set of ideas that tutors treat as basic for anyone going into medicine, mostly about evidence, that isn't on any A-level specification. This lesson covers:

• The A-level core, and how to revise it for an interview rather than an exam
• The principles that keep reappearing across topics
• Study design, and how to measure risk and benefit
• Which topics to know in depth beyond the syllabus, and where to read about them
• The other knowledge you will need: your personal statement and the general interview questions

If you know your A-level Biology and Chemistry thoroughly, you have the knowledge for nearly every science question. Download your exam board's specification and use it as a checklist: for each statement, ask whether you could explain it out loud accurately, and for the high-yield areas, why it happens (the first two levels in the next section). The table shows the areas that matter most and the direction interviews tend to take from each one. The right-hand column shows the kind of question to expect, not facts to learn.

Gaps in your specification

Exam boards differ, and interviews are in December of Year 13, before you have finished the course. The kidney, the nervous system, muscle contraction, the immune system and thermodynamics are all covered in different depth by different boards, or taught late. Check each high-frequency area above against your own specification. If yours doesn't cover one, or you haven't reached it, read the relevant chapter from a textbook for another board. You only need the A-level version.

If you don't take A-level Physics, make sure your GCSE physics is secure: pressure, current, voltage and resistance, waves and radiation. Tutors utilise these ideas freely, especially in questions on circulation, nerves and imaging.

Everything starts with knowing the A-level content accurately: what happens, in what order, with the right terms. That is the foundation, and it is the part to get completely secure, because you can't reason from knowledge you don't have. It helps to think of each topic at three levels.

Level 3 is what interviews are made of, but there are far too many possible variations to learn, and tutors deliberately choose ones you won't have seen. What you can do is practise working them out. Once a topic is secure, pose a few "what if" questions and reason through them out loud, then check your reasoning against a textbook. For example, once you know how a nerve impulse travels, ask what would happen if the sodium-potassium pump stopped, or if a toxin blocked the sodium channels, and work it out rather than looking it up. Doing this across a range of topics builds the habit you will use in the room.

As you revise, notice that the same few principles keep appearing in different topics: gradients, saturation, feedback, binding, scale. They are listed in the next section. Linking topics through them is what lets you answer a question about a system you haven't studied.

Underneath the topics, interview questions reuse a small number of principles. If you recognise which one a question is about, an unfamiliar question often turns into a familiar one. When you are stuck, go through this list and ask which principle applies.

None of this is on the A-level specification, beyond basic experimental design, but it comes up often. Tutors are scientists and doctors, medicine depends on evidence, and any "how would you test that?" or "would you trust this result?" question needs it.

The central problem: does X cause Y?

Most medical research tries to answer whether something (a drug, a habit, an exposure) causes an outcome. When two things are found together, there are four explanations other than causation, and a good answer considers each.

• Chance. In a small study, differences appear by luck. Larger studies and statistics deal with this.
• Bias. A systematic error in who is studied or how things are measured. If people with a disease are asked to remember past exposures, they search their memories harder than healthy people do (recall bias). If the healthiest patients are the ones offered a new treatment, it will look better than it is (selection bias).
• Confounding. A third factor linked to both. People who take vitamin supplements live longer, but they also tend to be richer, exercise more and smoke less. Any of those could explain the difference.
• Reverse causation. The outcome causes the exposure. People who are losing weight are more likely to die soon, but often because an undiagnosed illness is causing the weight loss.

The main study types

Qualitative studies, which use interviews or focus groups, answer a different kind of question: why and how rather than how many. Why do patients stop taking a medicine? What is it like to live with dialysis?

How a new treatment is tested

A new drug passes through a series of trials before and after it is approved, each answering a different question.

The hierarchy of evidence, and its limits

For questions about whether a treatment works, evidence is usually ranked by how well it protects against bias: systematic reviews of RCTs, then RCTs, then cohort studies, then case-control studies, then cross-sectional and ecological studies, then case reports and expert opinion.

The point that marks real understanding is that the best design depends on the question. You can't randomise people to smoke, so the evidence that smoking causes lung cancer comes from case-control and cohort studies. For a rare disease, a cohort study would need to follow enormous numbers of people, so a case-control study is the right tool. A first report of a new disease is a case series. If you are asked which design to use, start from what the question is and what would be ethical and practical, not from the top of the hierarchy.

What makes a trial fair

• A control group. Without one you can't tell the effect of the treatment from what would have happened anyway. Many conditions improve on their own.
• Placebo. People given an inactive treatment often improve, so a fair comparison is with a placebo, or with the current best treatment if one exists.
• Randomisation. Allocating by chance means the groups differ only by chance, in things you have measured and things you haven't.
• Blinding. If patients know which group they are in, their expectations affect results. If doctors know, their assessments can be biased. Double-blind means neither knows.
• Enough participants. Small trials miss real effects and exaggerate chance ones. The number needed is calculated before the trial starts.
• The right outcome, measured for long enough. It should be decided in advance and matter to patients. A drug that lowers blood pressure is useful only if it reduces strokes and heart attacks, and some effects take years to appear.
• Intention to treat. Patients are analysed in the group they were allocated to, even if they stopped the treatment. Otherwise people who drop out because of side effects vanish from the results and the treatment looks better than it is.
• Generalisability. Results from carefully selected volunteers may not apply to older patients or those with several conditions, who are often excluded.

Ethics of research

Participants give informed consent and can leave at any time. A trial is only ethical if there is genuine uncertainty about which option is better (equipoise). Studies are approved by an ethics committee, and an independent committee monitors results during a trial so it can be stopped early if one arm is clearly better or clearly harmful. A placebo should not be used where a proven treatment exists and withholding it would cause harm.

Statistics

You will have met p-values and confidence intervals at A-level, and they mean the same thing in a trial: a p-value below 0.05 means a difference this large would be unlikely if the treatment had no real effect, a confidence interval gives the range of plausible sizes for that effect, and a result can be statistically significant while being too small to matter to a patient.

Questions about treatments, trials and headlines depend on a few measures. Here is one example used throughout: over five years, 3% of people taking a placebo have a stroke, and 2% of people taking a new drug do.

"Cuts stroke risk by a third" and "prevents one stroke for every hundred people treated" describe the same result. Relative figures sound larger and are the ones that appear in headlines and adverts. Absolute figures are what an individual patient needs to make a decision, especially when weighed against side effects (the number needed to harm is calculated the same way). The same relative reduction gives a much bigger absolute benefit to someone at high risk than to someone at low risk, which is why treatments are often targeted at high-risk groups.

Case-control studies can't measure risk, because the researchers chose how many cases to include. They report an odds ratio instead, which is close to the relative risk when the disease is rare.

Some other terms that come up:

• Incidence is the number of new cases in a period. Prevalence is the number of people who have the condition at a given time. A disease that lasts a long time can have a high prevalence even if its incidence is low.
• Rates need a population and a time period: deaths per 1,000 people per year, for example. Comparing raw numbers of cases between groups of different sizes is a common mistake.
• Crude and age-standardised rates. A crude death rate depends heavily on how old a population is. Age-standardised rates adjust for this so that populations can be compared fairly.
• Morbidity is illness, and mortality is death.
• Life expectancy is calculated from the death rates at each age. A low average life expectancy can be driven largely by deaths in childhood.

Beyond the syllabus, aim to know one or two medical topics in real depth. Choose something you are genuinely interested in and immerse yourself in the science around it: how it works, what the evidence is, what is still unknown, and how it connects to the A-level content you already know. Depth comes across in an interview in a way that wide reading doesn't. An applicant who has followed one topic properly talks about it precisely, keeps reasoning when the tutor pushes past what they have read, and links it to other areas without being prompted.

These should be topics on your personal statement. Tutors read it, and often use something in it as the starting point for a question, so it is the one part of the interview you can predict. Anything you mention should be something you can discuss for ten minutes and reason about when the questions go further than your reading. The next section covers how to prepare each item on your statement.

Work through the sources in order, from the familiar to the specialist:

1. 1.Your A-level textbook. Start with the relevant chapter, and the equivalent chapter from another exam board if it goes further. Make sure the basics are secure before moving on.
2. 2.Writing for a general reader. A popular science book on the topic, or articles in magazines such as New Scientist or Scientific American, give the wider picture and the questions currently being asked.
3. 3.A university textbook chapter or a review article. A review article summarises the research on one topic, and many can be read free through PubMed Central or Google Scholar. Read only the chapter or review on your topic, not the whole book.
4. 4.One or two original research papers. Read the abstract, look at the figures, and ask the questions from the study design section: what kind of study it was, what was compared with what, and whether anything other than the authors' conclusion could explain the result.

By the end, for each topic, you should be able to explain the core science, the evidence for it, and one question that is still open.

Some things are not worth your time:

• First-year university content in general. Tutors choose questions nobody at school could already know the answer to, and if they sense you know one, they simply move on. Reading one chapter on a topic you care about is different from trying to get ahead on the course.
• Lists of diseases, drug names or unusual facts. If a question needs a specialist fact, the tutor will give it to you.
• Model answers to specific questions. The questions change every year, and a memorised answer falls apart at the first follow-up.

Time spent on any of these is better spent securing the A-level core and practising reasoning from it out loud.

Not everything you need to know is science. Two other areas come up in almost every Oxbridge medicine interview: your personal statement, which follows on from the reading above, and the general questions every medical school asks. Neither needs much explanation here, but both need to be part of your preparation from the start.

Your personal statement

Assume that anything in your personal statement can become the anchor for a science question: if you mention a book about antibiotic resistance, expect to be asked how resistance develops. For each book, project, EPQ or piece of work experience, prepare four things:

• What it was, in two sentences
• The one idea from it you found most interesting, and the science behind that idea
• Something that surprised you, or that you disagree with, and why
• A question it left you with

If there is anything you couldn't talk about for five minutes, find out more about it now.

The general interview questions

Questions on why you want to study medicine, ethical scenarios, the NHS and your work experience come up at both universities. At Cambridge they often have an interview of their own, and at Oxford they are usually part of each interview. Panels usually include a practising doctor, and Cambridge lists "awareness of the major current issues facing the NHS" among the things its interviewers assess. Don't treat this as secondary: prepare as thoroughly as you would for any other medical school interview. Our lessons on motivation for medicine, ethical questions, NHS and topical issues and work experience cover it, and you need it for your other three interviews anyway.

The difference at Oxbridge is that tutors follow up. Expect "why do you think that?" and "what would you say to someone who disagreed?" Prepared answers that you can't defend or extend do more harm than good, so focus on understanding your own views rather than memorising how to phrase them.