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Critical Appraisal. Or Making Reading More Worthwhile www.bradfordvts.co.uk. The Problem. Vast and expanding literature. Limited time to read. Different reasons to read – mean different strategies. Keeping up to date. Answering specific clinical questions. Pursuing a research interest. .

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critical appraisal

Critical Appraisal

Or Making Reading More Worthwhile

www.bradfordvts.co.uk

the problem
The Problem
  • Vast and expanding literature.
  • Limited time to read.
  • Different reasons to read – mean different strategies.
    • Keeping up to date.
    • Answering specific clinical questions.
    • Pursuing a research interest.

Bruce Davies

stages
Stages
  • Clarify your reasons for reading.
  • Specify your information need.
  • Identify relevant literature.
  • Critically appraise what you read.

Bruce Davies

clarify your reasons for reading
Clarify Your Reasons for Reading.
  • Keeping up to date.
    • Skimming the main journals and summary bulletins.
  • Answering specific clinical questions.
    • Finding good quality literature on subject.
  • Pursuing a research interest.
    • Extensive literature searching.

Bruce Davies

specify your information need
Specify Your Information Need.
  • What kind of reports do I want?
  • How much detail do I need?
  • How comprehensive do I need to be?
  • How far back should I search?
  • The answers to these questions should flow from the reasons for reading.

Bruce Davies

identify relevant literature
Identify Relevant Literature.
  • There are many ways of finding literature.
  • Remember to ask a librarian – they are the experts.
  • Selectivity is the key to successful critical appraisal.

Bruce Davies

critically appraise what you read
Critically Appraise What You Read.
  • Separating the wheat from the chaff.
  • Time is limited – you should aim to quickly stop reading the dross.
  • Others contain useful information mixed with rubbish.
  • Simple checklists enable the useful information to be identified.

Bruce Davies

questions to ask
Questions to Ask
  • Is it of interest?
  • Why was it done?
  • How was it done?
  • What has been found?
  • What are the implications?
  • What else is of interest?

Bruce Davies

questions to ask1
Questions to Ask
  • Is it of interest?
    • Title, abstract, source.
  • Why was it done?
    • Introduction.
      • Should end with a clear statement of the purpose of the study.
      • The absence of such a statement can imply that the authors had no clear idea of what they were trying to find out.
      • Or they didn’t find anything but wanted to publish!

Bruce Davies

questions to ask2
Questions to Ask
  • How was it done?
    • Methods.
      • Brief but should include enough detail to enable one to judge quality.
      • Must include who was studied and how they were recruited.
      • Basic demographics must be there.
      • An important guide to the quality of the paper.

Bruce Davies

questions to ask3
Questions to Ask
  • What has it found?
    • Results.
      • The data should be there – not just statistics.
      • Are the aims in the introduction addressed in the results?
      • Look for illogical sequences, bland statements of results.
      • ? Flaws and inconsistencies.
      • All research has some flaws – this is not nit picking, the impact of the flaws need to assessed.

Bruce Davies

questions to ask4
Questions to Ask
  • What are the implications?
    • Abstract / discussion.
      • The whole use of research is how far the results can be generalised.
      • All authors will tend to think their work is more important than the rest of us!
      • What is new here?
      • What does it mean for health care?
      • Is it relevant to my patients?

Bruce Davies

questions to ask5
Questions to Ask
  • What else is of interest?
    • Introduction / discussion.
      • Useful references?
      • Important or novel ideas?
      • Even if the results are discounted it doesn’t mean there is nothing of value.

Bruce Davies

what is the method
What Is the Method?
  • The first task – alternative check lists for different methods.
  • How was the study conducted to confirm the method?
  • Authors sometimes use the wrong words to describe their work!

Bruce Davies

surveys
Surveys
  • Describe how things are now.
  • Samples of populations or special groups.
  • The samples must be randomly selected.

Bruce Davies

surveys1
Surveys
  • Do not have separate control or comparison groups.
    • Comparisons may be made between subgroups – but this is not control.
  • Use of the term survey should identify the method – beware the use in what is really a cohort study.

Bruce Davies

surveys2
Surveys
  • Cross-sectional is seldom used to describe other methods.
  • There are many ways of selecting a sample: e.g: stratified, cluster and systematic.

Bruce Davies

cohort studies
Cohort Studies
  • Used to find out what happens to patients.
  • A group is identified and then watched to see what events befall them.
  • May have comparison or control groups – who must be identified from the start.
    • Not an essential feature tho.’

Bruce Davies

cohort studies1
Cohort Studies
  • Must have the element of time flowing forward, from the point at which they are identified.
  • This is sometimes called a retrospective cohort study.
  • The term cohort should be diagnostic.

Bruce Davies

clinical trials
Clinical Trials
  • Testing.
  • Always concerned with effectiveness.
  • The focus should always be on the outcome.
    • The outcomes may not be beneficial – in other words side effect trials.
  • Sometimes cohort trials are used to assess effectiveness. This is very poor research and can usually be dismissed.

Bruce Davies

clinical trials1
Clinical Trials
  • When more than two things are compared it makes the study more complex and harder to get right.
  • The key words to look for are: random allocation, double blind, single blind, placebo-controlled.
  • The term outcome is sometimes used in cohort studies as well.

Bruce Davies

case control studies
Case-control Studies
  • Ask what makes groups of patients different.
  • Select a set of patients with a characteristic – eg a disease.
  • The characteristics of this set are then compared with a control group who do not have the characteristic being studied – but all all other respects must be as identical as possible.

Bruce Davies

case control studies1
Case-control Studies
  • Case studies look backward – not forward as cohort studies do.
  • Other terms used are: case-referrent, case-comparator, case-comparison.
  • May also be called retrospective – as is used for some cohort studies.

Bruce Davies

the results
The Results
  • The major mental challenge.
  • What do I think this really means?
  • CAUTION.
    • Large unexpected results are rare.
    • Flawed studies and misleading findings are common.

Bruce Davies

statistics
Statistics
  • A subject in itself.
  • Some general thoughts are worth emphasising.

Size matters.

Bruce Davies

probability
Probability
  • Is just that.
  • It is not proof.
  • Think of horse racing and the lottery.
  • Think of the odds.

Bruce Davies

pitfalls
Pitfalls
  • All statistical tests make assumptions about the raw data.
  • If there is no raw data presented you cannot know if the tests are meaningful.
  • Outliers.

Bruce Davies

pitfalls1
Pitfalls
  • Skew.
  • Non-independence.
  • Serendipity masquerading as hypothesis – or data trawling!

Bruce Davies

pitfalls2
Pitfalls
  • Black box analyses. Modern computers make statistical testing easy – the authors may not know what they are doing!
  • Bias – play devils advocate.
  • Confounding.
    • A very common problem in medicine.
    • Colour televisions do not cause increases in hypertension.

Bruce Davies

checklists
Checklists
  • Checklists for particular types of literature are a quick and easy way of learning critical appraisal.
  • They all have 3 stages:
    • Basic questions.
    • Essential appraisal.
    • Detailed appraisal.

Bruce Davies

but but but
BUT, BUT, BUT
  • Checklists do not tell you about the quality or usefulness.
  • This is still a subjective question.
  • All the lists do is enable a more structured and thoughtful response to the subjective question.

Bruce Davies

references
References
  • The Pocket guide to critical appraisal.
    • By: Iain Crombie.
    • Pub BMJ Books, 1996.
  • How to lie with statistics.
    • By: Darrell Huff.
    • Pub: Pelican, 1989.

Bruce Davies