critical reading st helier vts 2008 rcgp curriculum core statement domain 3 as
TRANSCRIPT
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CRITICAL READING
ST HELIER VTS 2008RCGP Curriculum Core Statement Domain 3
AS
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What is expected….
• Hierarchy of evidence• Statistical terms• Data Presentation• Seminal trials
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What is expected….
• Mean, median, mode• Normal distribution curve, std deviation• ARR, RRR• NNT, NNH• P value, confidence intervals• Sensitivity, specificity• PPV, NPV
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Critical Reading
• Critical Appraisal– Look at the specific objectives, methods, and
results of the study
• Critical reflection– Judge and discuss the implications for the world
outside the study
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Critical Appraisal
• Title, author, institute, journal
• Ethics
• References
• Conflicts of interests
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Critical Appraisal
• Introduction– Background– Aims– Relevance– Originality
• Methods– Design– Outcome measures– Subjects
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Design
• Time Frame• Prospective• Cross-Sectional• Retrospective
• Observational / Interventional• Controlled / Uncontrolled• Randomised / Non-randomised
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Bias
• Selection Bias– Typical sample?– Exclusions (numbers and reasons) clear?– Same conditions for both groups
• Measurement Bias– Observer error– Validity– Reliability
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Bias
• Validity – closeness to true measure– Internal – Can I believe the results?– External – If I can, do they apply to the real world?
• Reliability – repeatability of the measurements
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Implications
• Generalisation• Consequences
• PPeople and ethics• RResources• AAudit protocols and quality• TTime and training• SSafety and society
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Critical Appraisal
• Presentation• Experimental Design• Numbers• Information Bias• Selection Bias
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Summarising A Paper
• General aim – one sentence why the study was done
• Objective – what was the specific aim of the study?
• Design• Setting – where was the study done?
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Summarising a Paper
• Population• Target• Sampling frame• Study population
• Methods• Intervention• Baseline• Outcome
• Results• Author’s conclusions – main points
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Does treatment work?
• Consider the DCCT Trial
• Incidence of Neuropathy is 9.6% in control group (CER)
• Intervention group (6yrs very tight control) is 2.8% (EER)
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Does treatment work?
• Relative risk reduction is:
9.6%-2.8% 9.6% equals 71%
• Absolute risk reduction is:
9.6% - 2.8% equals 6.8%
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RRR
• Same result if 96% got neuropathy in the control group and 28% in intervention group
• Fails to show baseline risk or size of effect• Tiny effect can look impressive
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NNT
• Inverse of ARR• 100/6.8%=14.7, i.e. treat 15 patients for 6
years to prevent one extra neuropathy
• Practical result• Easier to compare treatments• Beware intention to treat figures
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Screening
• Sensitivity %age with +ve test result• High if few missed
• Specificity %age with true negative result• High if few false alarms
• Predictive value proportion of +ve results who have condition
• Depends on prevalence
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Odds Ratios
• Ratio of events in intervention group v control group
• Forest plot• 1 means no effect• CI including 1 – no effect• Further away from 1, more likely a true effect
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PPV and NPV
• Positive Predictive Value
• Ability of test to pick out disease
– Eg 160 positive results from a diseased population of 200:
160/200 = 80% PPV
• Negative Predictive Value
• Ability of test to pick out those who do not have disease– Eg 70 negative results
from a healthy population of 100:70/100 = 70% PPV
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Qualititive studies
• Studying ideas and concepts• Narrative based medicine• Understanding patient• Turns anecdotes into data/observations
• Passive observation of behaviour• Participation Groups• One to One interviews• Focus Groups• Document Studies
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Systematic Reviews
• Does the review examine an important clinical question
• Was there a substantial effort to search all relevant literature
• Was methodological quality assessed and trials weighted accordingly
• How sensitive are the results to the way the review has been done
• Have the results been interpreted with common sense and due regard to the broader issues
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RCT
• Expensive• Time-consuming• Small numbers (usually)• Subjects and settings limit generalisation of
results• Random allocation cannot overcome bias –
Intention to treat, drop-out rates etc
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Audit
• Systematic survey with a purpose that requires repeating
• More than a survey as part of process of change– Uncontrolled observational study that may
become an uncontrolled prospective interventional study
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ASCOT
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Summary of all end points
The area of the blue square is proportional to the amount of statistical information
Amlodipine perindopril better Atenolol thiazide better0.50 0.70 1.00 1.45
Primary
Non-fatal MI (incl silent) + fatal CHD
SecondaryNon-fatal MI (exc. Silent) +fatal CHDTotal coronary end pointTotal CV event and proceduresAll-cause mortalityCardiovascular mortalityFatal and non-fatal strokeFatal and non-fatal heart failure
Tertiary Silent MIUnstable anginaChronic stable anginaPeripheral arterial diseaseLife-threatening arrhythmiasNew-onset diabetes mellitusNew-onset renal impairment
Post hoc Primary end point + coronary revasc procsCV death + MI + stroke
2.00
Unadjusted Hazard ratio (95% CI)
0.90 (0.79-1.02)
0.87 (0.76-1.00)0.87 (0.79-0.96)0.84 (0.78-0.90)0.89 (0.81-0.99)0.76 (0.65-0.90)0.77 (0.66-0.89)0.84 (0.66-1.05)
1.27 (0.80-2.00)0.68 (0.51-0.92)0.98 (0.81-1.19)0.65 (0.52-0.81)1.07 (0.62-1.85)0.70 (0.63-.078)0.85 (0.75-0.97)
0.86 (0.77-0.96)0.84 (0.76-0.92)
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Adverse events leading to treatment discontinuation
Adverse eventAmlodipine perindopril
(%)
Atenolol thiazide(%)
Total 2358 (24.5) 2402 (25.0)
Serious 162 (1.7) 254 (2.6)*
* p<0.0001