CRITICAL READING ST HELIER VTS 2008 RCGP Curriculum Core Statement Domain 3 AS

What is expected…. Hierarchy of evidence Statistical terms Data Presentation Seminal trials

What is expected…. Mean, median, mode Normal distribution curve, std deviation ARR, RRR NNT, NNH P value, confidence intervals Sensitivity, specificity PPV, NPV

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

Critical Appraisal Title, author, institute, journal Ethics References Conflicts of interests

Critical Appraisal Introduction – Background – Aims – Relevance – Originality Methods – Design – Outcome measures – Subjects

Design Time Frame Prospective Cross-Sectional Retrospective Observational / Interventional Controlled / Uncontrolled Randomised / Non-randomised

Bias Selection Bias – Typical sample? – Exclusions (numbers and reasons) clear? – Same conditions for both groups Measurement Bias – Observer error – Validity – Reliability

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

Implications Generalisation Consequences P People and ethics R Resources A Audit protocols and quality T Time and training S Safety and society

Critical Appraisal Presentation Experimental Design Numbers Information Bias Selection Bias

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?

Summarising a Paper Population Target Sampling frame Study population Methods Intervention Baseline Outcome Results Author’s conclusions – main points

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)

Does treatment work? Relative risk reduction is: 9.6%-2.8% 9.6%equals71% Absolute risk reduction is: 9.6% - 2.8%equals6.8%

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

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

Screening Sensitivity%age with +ve test result High if few missed Specificity%age with true negative result High if few false alarms Predictive valueproportion of +ve results who have condition Depends on prevalence

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

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

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

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

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

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

ASCOT

Summary of all end points The area of the blue square is proportional to the amount of statistical information Amlodipine  perindopril better Atenolol  thiazide better Primary Non-fatal MI (incl silent) + fatal CHD Secondary Non-fatal MI (exc. Silent) +fatal CHD Total coronary end point Total CV event and procedures All-cause mortality Cardiovascular mortality Fatal and non-fatal stroke Fatal and non-fatal heart failure Tertiary Silent MI Unstable angina Chronic stable angina Peripheral arterial disease Life-threatening arrhythmias New-onset diabetes mellitus New-onset renal impairment Post hoc Primary end point + coronary revasc procs CV death + MI + stroke 2.00 Unadjusted Hazard ratio (95% CI) 0.90 ( ) 0.87 ( ) 0.87 ( ) 0.84 ( ) 0.89 ( ) 0.76 ( ) 0.77 ( ) 0.84 ( ) 1.27 ( ) 0.68 ( ) 0.98 ( ) 0.65 ( ) 1.07 ( ) 0.70 ( ) 0.85 ( ) 0.86 ( ) 0.84 ( )

Adverse events leading to treatment discontinuation Adverse event Amlodipine  perindopril (%) Atenolol  thiazide (%) Total2358 (24.5)2402 (25.0) Serious162 (1.7)254 (2.6)* * p<0.0001