CRITICAL READING

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 • People and ethics • Resources • Audit protocols and quality • Time and training • 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% equals 71% • Absolute risk reduction is: 9.6% - 2.8% equals 6.8%

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 value proportion 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 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) PrimaryNon-fatal MI (incl silent) + fatal CHD SecondaryNon-fatal MI (exc. Silent) +fatal CHD Total coronary end pointTotal CV event and proceduresAll-cause mortalityCardiovascular mortalityFatal and non-fatal strokeFatal and non-fatal heart failure TertiarySilent MI Unstable anginaChronic stable anginaPeripheral arterial diseaseLife-threatening arrhythmiasNew-onset diabetes mellitusNew-onset renal impairment Post hoc Primary end point + coronary revasc procs CV death + MI + stroke 1.00 1.45 2.00 0.50 0.70 Atenolol  thiazide better Amlodipine  perindopril better The area of the blue square is proportional to the amount of statistical information

Adverse events leading to treatment discontinuation * p<0.0001

CRITICAL READING