how to read a medical paper: part 1, is this a good paper?

How To Read a Paper

Otherwise known as A BREAK FROM STATISTICS

Dr Luke Kane April 2014

Great Reference:

• BMJ - How to read a paper• Greenhalgh, T. (1997) “How to read a

paper” British Medical Journal. Web, accessed April-May 2014 at http://www.bmj.com/about-bmj/resources-readers/publications/how-read-paper

• Lecture based on T Greenhalgh’s papers, available above

Outline

• IMRAD - the structure of the paper• How to work out if the paper is worth reading• Critical appraisal:

– Why was the study done?– What type of study was done?– Was the design appropriate to the research?

• Hierarchy of evidence• Terms to understand• Peer Review• Rejection!

IMRAD

• Introduction (why the authors decided to do this research)

• Methods (how they did it, and how they analysed their results)

• Results (what they found)• Discussion (what the results mean)

Is This Paper Worth Reading?

• This will be answered by looking at the design of the methods section

• As tempting as it may be:• Not on the interest of the hypothesis• Not on the nature or potential impact

of the results• Not on the speculation in the

discussion

Critical Appraisal

• The assessment of methodological quality

• Q1: Why was the study done? • Q2: What type of study is it?• Q3: Is the study design appropriate?

Q1: Why was the Study done?

• Introductory sentence of a research paper should state what the background to the research is

• For example, “Appendix removal is a common procedure in children, and it has been suggested that not all operations are clinically necessary.”

• This statement should be followed by a brief review of the published literature

Q1: Why has the study been done?

• Unless mentioned in the introduction, the hypothesis should be clearly stated in the methodology section

• If it is phrased as a negative then it is known as the null hypothesis

Q2: What type of study was done?

• First, decide whether the paper describes a primary study or a secondary study

• A primary study reports research first hand

• A secondary (also known as integrative) study tries to summarise and draw conclusions from primary studies

Q2: What type of study was done?

• Primary studies are one of 3 types:1.Experiments: in which a manoeuvre is

performed on an animal/volunteer 2.Clinical trials: in which an intervention,

such as a drug treatment, is offered to a group of patients who are followed up to see what happens

3.Surveys: something is measured in a group of patients

Secondary Studies

• Secondary studies can be divided up into: • OVERVIEWS

– Non-systematic: summary of primary studies– Systematic: As above but strict methodology– Meta-analysis: Summarise numerous primary studies

• GUIDELINES: draw conclusions about how clinicians should practice

• DECISION ANALYSES: use primary studies to make probabililty tree to help make decisions

• ECONOMIC ANALYSES: use primary studies to determine whether something is worth the money

Q3: Was the design appropriate to the Research?

• Consider which broad field of research the design is from:

• Therapy: testing the efficacy of drug treatments, surgical procedures, alternative methods of service delivery, or other interventions. Preferred study design is randomised controlled trial

• Diagnosis: demonstrating whether a new diagnostic test is valid (can we trust it?) and reliable (would we get the same results every time?). Preferred study design is cross sectional survey in which both the new test and the gold standard are performed

Q3: Was the design appropriate to the Research?

• Screening: demonstrating the value of tests which can be applied to large populations and which pick up disease at a presymptomatic stage. Preferred study design is cross sectional survey

• Prognosis: determining what is likely to happen to someone whose disease is picked up at an early stage. Preferred study design is longitudinal cohort study

• Causation: determining whether a putative harmful agent, such as environmental pollution, is related to the development of illness. Preferred study design is cohort or case-control study, depending on how rare the disease is, but case reports may also provide crucial information

Hierarchy of Evidence

1.Systematic reviews and meta-analyses2.Randomised controlled trials3.Cohort studies4.Case-control studies5.Cross sectional surveys6.Case reports

Terms to Understand

• Parallel group comparison: Each group receives a different treatment, with both groups being entered at the same time; results are analysed by comparing groups

• Paired (or matched) comparison: Subjects receiving different treatments are matched to balance potential confounding variables such as age and sex; results are analysed in terms of differences between subject pairs

• Within subject comparison: Subjects are assessed before and after an intervention and results analysed in terms of changes within the subjects

Terms to Understand

• Single blind: Subjects did not know which treatment they were receiving

• Double blind: Neither did the investigators• Crossover: Each subject received both the intervention

and control treatments (in random order), often separated by a washout period with no treatment

• Placebo controlled: Control subjects receive a placebo (inactive pill) which should look and taste the same as

the active pill. Placebo (sham) operations may also be used in trials of surgery

Terms to be Aware of

• Factorial design: A study which permits investigation of the effects (both separately and combined) of more than one independent variable on a given outcome (for example, a 2x2 factorial design tested the effects of placebo, aspirin alone, streptokinase alone, or aspirin plus streptokinase in acute heart attack)

Peer Review

• This is when a paper is submitted to a journal and the journal arranges for "peers", i.e. experts, to see if the paper reaches a certain standard

Rejection!

• The study did not address an important scientific issue

• The study was not original (someone else had already done the same or a similar study)

• The study did not actually test the authors' hypothesis

• A different type of study should have been done

Rejection!

• Practical difficulties (in recruiting subjects, for example) led the authors to compromise on the original study protocol

• The sample size was too small• The study was uncontrolled or inadequately controlled• The statistical analysis was incorrect or inappropriate• The authors drew unjustified conclusions from their data• There is a significant conflict of interest (one of the

authors, or a sponsor, might benefit financially from the publication of the paper and insufficient safeguards were seen to be in place to guard against bias)

• The paper is so badly written that it is incomprehensible• RET

Questions!

• THANKS

References

• Grant, A. (2014) “Epidemiology for tropical doctors”. Lecture (S6) from the Diploma of Tropical Medicine & Hygiene, London School of Hygiene & Tropical Medicine.

• Greenhalgh, T. (1997) “How to read a paper” British Medical Journal. Web, accessed April-May 2014 at <http://www.bmj.com/about-bmj/resources-readers/publications/how-read-paper>