How to Write Single Best Answer (SBA) Questions

Most undergraduate and postgraduate medical examinations of knowledge now use the single best answer (SBA) format for multiple-choice questions.

Writing good single best answer questions can be challenging. This guide covers how to write high-quality SBA questions and some common problems when writing SBAs. 

What is a single best answer question?

A single best answer question has a clinical scenario (the stem), a question, and five answer options.

Unlike traditional MCQs, the incorrect answers (distractors) may be plausible or partially correct. However, the correct answer is the ‘best’ answer to the scenario and posed question. The candidate has to use higher order thinking and reasoning skills to identify the correct answer, instead of just relying on factual recall. 

Question structure and content

Stem structure

The stem should contain only information that is relevant and avoid the inclusion of superfluous clinical details.

The stem should be structured as follows (making sure to only information relevant to the question i.e. if vital signs don’t have any importance, exclude them):

• Patient details (gender/age)
• Presenting complaint (PC)
• History of presenting complaint (HPC)
• Relevant past medical history, family history and social history
• Observations/Vitals /GCS
• Physical examination findings
• Results (e.g. laboratory / radiology)

Acceptable question style

Ask for the BEST answer, NOT one that is TRUE/FALSE, for example:

• ‘What is the most likely diagnosis?’
• ‘What is the most appropriate initial management step?’
• ‘Which of the following investigations would be most useful in reaching a definitive diagnosis?’
• ‘Which of the following investigations would be most appropriate to perform first?’

Check your question passes the “best practice cover test” – the candidate should be able to answer the question solely from the stem of the question, with the answer options covered.

Things to avoid

• The inclusion of irrelevant background information.
• The inclusion of the reader in the question (e.g. “You are a junior doctor working in A&E when a 37-year-old patient presents with…”) – a better format would be (e.g. “A 37-year-old male presents to the A&E department with…”).
• The use of negative questions (e.g. ‘What is the LEAST likely diagnosis’).

Answer options

Tips for writing high-quality answer options:

• Provide 5 succinct answer options.
• Answer options should be homogeneous (e.g. they should all be a diagnosis/treatment/anatomical location etc)
• All answer options should be plausible and familiar, but one should be BETTER than the others.
• The correct answer(s) should be evidence-based and widely agreed upon by experts (e.g. NICE guidance).

Explanation

Structure and formatting

Identify and explain the correct answer

The explanation should first identify the correct answer and explain why this is the most appropriate answer. You should provide some educational value relating to the answer (i.e. if the answer was a diagnosis, you would explain what the diagnosis is, how it typically presents etc).

Move on to explain why the other answer options were less correct/wrong

After explaining the correct answer, the explanation should then move on to discuss why the other possible answers were less correct. You should briefly explain each of the incorrect answers where possible (e.g. if they are diagnoses, you would briefly describe how each might typically present). 

Example of a good question

Question

Sandy Hughes, 67, presents to A&E with chest pain. She describes 12 hours of sharp chest discomfort on inspiration, which started suddenly just after she arrived back from her flight to Florida. Her oxygen saturation is 94% on 2 litres of oxygen and her respiratory rate is 28.

What is the most likely ECG finding for this patient?

Answers

• Right axis deviation
• SI QIII TIII pattern
• Sinus tachycardia
• ST elevation in three contiguous leads
• Widespread saddle-shaped ST elevation

Explanation

The most likely ECG finding in this patient is sinus tachycardia. This patient has presented with the classic signs of a pulmonary embolism (PE)- recent travel, sudden onset chest pain which is worse on inspiration, and increased respiratory rate with low oxygen saturations. ECG findings in PE can include right axis deviation, sinus tachycardia, and the oft-mentioned but rarely seen SI QIII TIII pattern. Of these, the most likely is sinus tachycardia. ST elevation in three contiguous leads would be seen in an ST-elevation myocardial infarction rather than a PE, and widespread saddle-shaped ST elevation is indicative of pericarditis.

Further reading 

https://patient.info/doctor/pulmonary-embolism-pro

What makes this a good question?

The information in the stem is relevant and is written in a clear manner. This is a two-step question which is slightly more challenging- the reader must first choose a likely diagnosis for the patient, and then consider subsequent ECG findings. None of the answers are ‘wrong’- all could be seen in a patient with chest pain. However, the best candidate would rule out findings not seen in PE and then choose (as the question asks) the most likely ECG finding.  The explanation is informative and explains which of the answers are more or least likely, and why. The answer is also referenced for further information.

Examples of some low-quality questions

Example 1

Question

A male patient presents to his GP with a cough. The patient describes feeling unwell.  They have a past medical history of an appendectomy.

What is the most likely diagnosis?

Answers

• COPD
• Hypersensitivity pneumonitis
• Lung cancer
• Pneumonia
• Tuberculosis

Explanation

The correct answer is pneumonia, as it is statistically the most likely diagnosis in a patient presenting to their GP with a cough.

Why is this a poor quality question?

The stem is vague – in order to correctly answer the question, the reader would need more details such as the patient’s age, related symptoms, smoking history, occupational history, travel history, etc. The past medical history of an appendectomy is entirely irrelevant to the stem. The patient could have any of the above conditions – all may present with a cough and “feeling unwell”. Of course, statistically speaking, pneumonia is likely the most common diagnosis made in someone presenting to their GP with a cough. However, this question isn’t testing any diagnostic skills in the reader. Questions should be asking what the most likely diagnosis is in a patient given the information and background provided.

Example 1 reworked

Question

A male patient, aged 73, presents to his GP with a six-week history of a cough. The patient also describes feeling ‘run down’ lately and has lost weight. He has on occasion coughed up some blood. The patient has a smoking history of 80 pack-years.

What is the most likely diagnosis?

Answers

• COPD
• Hypersensitivity pneumonitis
• Lung cancer
• Pneumonia
• Tuberculosis

Explanation

The most likely diagnosis in this patient is lung cancer. All of the above conditions could present with a cough, however, only tuberculosis and lung cancer are likely to present with haemoptysis and weight loss as well. The patient’s smoking history, combined with no known history of fevers or other risk factors, makes lung cancer the most likely diagnosis in this patient.

Further information

https://patient.info/doctor/lung-cancer-pro

Example 2

Question

Which joint disease is associated with morning stiffness that improves with activity?

Answers

• Ankylosing spondylitis
• Gout
• Osteoarthritis
• Rheumatoid arthritis

Why is this a poor quality question?

It is in a multiple-choice rather than single best answer format. There is no clinical vignette or background information, and there are only four options for answers rather than five. Additionally, morning stiffness is seen in both rheumatoid arthritis and ankylosing spondylitis.

Example 2 reworked

Question

Alice McAvey, 51, has presented to rheumatology outpatients with pain in her hands. She describes five weeks of pain and stiffness in her joints in the morning, lasting around 30 minutes. Her pain often improves with some light activity.

What is the most likely diagnosis in this patient?

Answers

• Ankylosing spondylitis
• Gout
• Osteoarthritis
• Psoriatic arthritis
• Rheumatoid arthritis

Explanation

The correct answer is rheumatoid arthritis. All of the above conditions cause joint pain, however only ankylosing spondylitis, psoriatic arthritis, and rheumatoid arthritis are associated with morning stiffness. Ankylosing spondylitis is known to affect the spine, not the hands. Given that there is no known history of psoriasis in this patient, rheumatoid arthritis is the most likely answer. Gout and osteoarthritis are less likely to be symmetrical in presentation, and would not present with morning stiffness.

Further information

https://patient.info/doctor/rheumatoid-arthritis-pro

Questions?

If you have any questions or suggestions of things to add to this guide, please don’t hesitate to get in touch via [email protected].