Contents

Introduction

Definition of evidence-based medicine

Asking answerable questions

Patient or problem

Intervention

Comparison intervention

Outcome

Type of question

Finding the evidence: how to get the most from your searching

Convert your question to a search strategy

Critical appraisal of guidelines

Scope and purpose of the guideline

Methods

Applicability

Conflict of interest

Appraising systematic reviews

Is the systematic review valid?

Are the results important?

How precise are the results?

Appraising diagnosis articles

Is the study valid?

Are the results important?

Summary

Nomogram for likelihood ratios

Appraising articles on harm/aetiology

Is the study valid?

Are the results important?

Appraising prognosis studies

Is the study valid?

Are the results important?

Appraising therapy articles

Is the study valid?

Are the results important?

Appraising qualitative studies

Appraising economic evaluations

Does this economic evaluation provide a valid comparison of alternatives?

Applying the evidence

Are your patients similar to those of the study?

How much of the study effect can you expect for your patient(s)?

Is the intervention realistic in your setting?

Does the comparison intervention reflect your current practice?

What alternatives are available?

Are the outcomes appropriate to your patient?

Evidence-based medicine: glossary of terms

Selected evidence-based healthcare resources on the web

Levels of evidence

Study designs

Case-control study

Cohort study

Crossover design

Cross-sectional survey

Diagnostic validation study

Randomized controlled trial (RCT)

Index

© 2002 BMJ Books

© 2006 Carl Heneghan and Douglas Badenoch

Published by Blackwell Publishing Ltd

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First published 2002

Second edition 2006

1 2006

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Introduction

This ‘toolkit’ is designed as a summary and reminder of the key elements of practising evidence-based medicine (EBM). It has largely been adapted from resources developed at the Centre for Evidence-based Medicine. For more detailed coverage, you should refer to the other EBM texts and web pages cited throughout.

The first page of each chapter presents a ‘minimalist’ checklist of the key points. Further sections within each chapter address these points in more detail and give additional background information. Ideally, you should just need to refer to the first page to get the basics, and delve into the further sections as required.

Occasionally, you will see the dustbin icon on the right. This means that the question being discussed is a ‘filter’ question for critical appraisal: if the answer is not satisfactory, you should consider ditching the paper and looking elsewhere. If you don’t ditch the paper, you should be aware that the effect it describes may not appear in your patient in the same way.

Definition of evidence-based medicine

Evidence-based medicine is the ‘conscientious, explicit and judicious use of current best evidence in making decisions about individual patients’.

This means ‘integrating individual clinical expertise with the best available external clinical evidence from systematic research’ (Sackett et al. 2000).

We can summarize the EBM approach as a five-step model:

Asking answerable questions

The four elements of a well-formed clinical question are:

The terms you identify from this process will form the basis of your search for evidence and the question as your guide in assessing its relevance.

Bear in mind that how specific you are will affect the outcome of your search: general terms (such as ‘heart failure’) will give you a broad search, while more specific terms (for example, ‘congestive heart failure’) will narrow the search.

Also, you should think about alternative ways or aspects of describing your question (for example, New York Heart Association Classification).

Patient or problem

First, think about the patient and/or setting you are dealing with. Try to identify all of their clinical characteristics that influence the problem, which are relevant to your practice and which would affect the relevance of research you might find. It will help your search if you can be as specific as possible at this stage, but you should bear in mind that if you are too narrow in searching you may miss important articles (see next section).

Intervention

Next, think about what you are considering doing. In therapy, this may be a drug or counselling; in diagnosis it could be a test or screening programme. If your question is about harm or aetiology, it may be exposure to an environmental agent. Again, it pays to be specific when describing the intervention, as you will want to reflect what is possible in your practice. If considering drug treatment, for example, dosage and delivery should be included. Again, you can always broaden your search later if your question is too narrow.

Comparison intervention

What would you do if you didn’t perform the intervention? This might be nothing, or standard care, but you should think at this stage about the alternatives. There may be useful evidence which directly compares the two interventions. Even if there isn’t, this will remind you that any evidence on the intervention should be interpreted in the context of what your normal practice would be.

Outcome

There is an important distinction to be made between the outcome that is relevant to your patient or problem and the outcome measures deployed in studies. You should spend some time working out exactly what outcome is important to you, your patient, and the time-frame that is appropriate. In serious diseases it is often easy to concentrate on the mortality and miss the important aspects of morbidity. However, outcome measures, and the relevant time to their measurement, may be guided by the studies themselves and not by your original question. This is particularly true, for example, when looking at pain relief, where the patient’s objective may be ‘relief of pain’ while the studies may define and assess this using a range of different measures.

Type of question

Once you have created a question, it is helpful to think about what type of question you are asking, as this will affect where you look for the answer and what type of research you can expect to provide the answer.

Typology for question building

Template for asking answerable clinical questions

Deciding which question to ask:

Further reading

Educational Prescriptions: http://www.cebm.net

Gray J. Doing the right things right. In: Evidence Based Health-Care. New York: Churchill Livingstone, 1997, chapter 2.

Richardson W, Wilson M, Nishikawa J, Hayward RS. The well-built clinical question: a key to evidence-based decisions [editorial]. ACP J Club 1995;123:A12–13.

Sackett DL, Rosenberg WMC, Gray JAM, Haynes RB, Richardson WS. Evidence based medicine: what it is and what it isn’t. Br Med J 1996;312:712.

Sackett DL, Straus SE, Richardson WS, Rosenberg WMC, Haynes RB. Evidence-Based Medicine: How to practice and teach EBM, 2nd Edn. New York: Churchill Livingstone, 2000.

Finding the evidence: how to get the most from your searching

Convert your question to a search strategy

Identify terms that you would want to include in your search:

Generally, it helps you to construct a search for each concept separately, then combine them.

Think about what kind of evidence you need to answer your question:

1 Try these first

These sources will give you the best return on your precious time.

2 Secondary sources

Of course, if someone has already searched for and appraised evidence around your question, it makes sense to use that information if possible.

A note about guidelines

An authoritative, evidence-based guideline would give you the best starting point for your search. However, we have assumed that your questions tend to be the ones that aren’t answered by the guidelines. Also, it’s important to bear in mind that not all guidelines are ‘evidence-based’ (Grimshaw 1993; Cluzeau 1999).

Good sources include:

Can I trust this secondary source?

Only if you can answer ‘yes’ to all of the following:

Critically appraised topics (CATs)

CATs are appraisals of the evidence found in response to a clinical question. They are a very useful way of organizing your own appraisals and sharing them with your colleagues. Many people use them to help run evidence-based journal clubs. Many people now make their CATs available on the web and you might like to start searching here. You should be wary, however, of the provenance of these CATs.

Evidence-based summaries