Critical Appraisal Quiz!

P(There will be prizes) <0.05

Which one of the following best describes absolute risk increase?

A. Control event rate (CER) – experimental event rate (EER)

B. CER + EERC. EER – CERD. The likelihood of a positive resultE. The proportion of positives accurately

diagnosed with a disorder

C

Which of the following best describes the term external validity?

A. The agreement between two raters using the same test at the same time

B. The consistency of a measure used on two separate occasions

C. The extent to which one can appropriately apply the results to other populations

D. The level of agreement between two or more raters using the same test on two or more occasions

E. The level of consistency between two separate halves of the same test

C

Which of the following describes a cohort study?

A. A study that aims to establish the normal height of 4yr old children by measuring height as school entry

B. A study that compares a group of children who’s heights are below the tenth centile with a group of matched controls of normal height aiming to identify possible causative factors

C. A study that compares two groups of 4yr olds with similar characteristics: one group is given a drug and the other a placebo and the growth of each group is measured following this intervention

D. A study that compares the height of a group of 4yr olds living near a nuclear plant with the height of a group of 4yr olds who live elsewhere

E. A study that looks a all children born at one hospital in one year and measures their height at intervals up to four years of age

Cross-sectional

Case-control

Cohort

Controlled Trial

Longitudinal

Longitudinal; case-control; controlled trial; cross-sectional

A hierarchy of quality in evidence based medicine exists, with study types ranked according to the

strength of their data

Which one of the following correctly ranks the study types with the most robust first and the least robust

last?

A. RCT, CR, CC, MAB. MA, RCT, CC, CRC. RCT, CR, MA, CCD. CR, CC, MA, RCTE. RCT, CC, MA, CR

Case report (CR)Randomised double-blind placebo controlled trial (RCT)

Case-control study (CC)Meta-analysis (MA)

B

EMQ – Study types

A. Case-controlB. Case reportC. Cohort StudyD. Double-blind, randomised,

placebo-controlled trialE. Meta-analysisF. Qualitative StudyG. Single-blinded, randomised,

placebo-controlled trial

1. The Framington Heart study2. The Cochrane Collaboration3. The Scandinavian Simvastatin

Survival Study4. A trial of sham acupuncture for

period pains in which patients are allocated randomly to treatment or placebo

5. A study of patient’s experiences of berevement

A new test to screen for CF carriers is being considered. Preliminary results for the test in 100 children, in comparison with the gold standard of chromosome analysis, are shown

below

A. The accuracy of the test is 91%B. The new test is better than the GSC. Positive predictive value is 80%D. The sensitivity is 80%E. The specificity is 87%

positive chromosome analysis

negative chromosome analysis

New test positive 4 8

New test negative 1 87

TFFTF

That last slide explained…

• Accuracy – proportion of tests with correct results = a+d/a+b+c+d = 91/100 = 91%

• Sensetivity – the true positive rate = a/a+c = 4/5 = 80%• Specificity – the true negative rate = d/b+d = 87/95 = 92%• Positive predictive value – the probability of having the

condition once test is +ve = a/a+b = 4/12 = 33%• Negative predictive value – probability of having

condition once test is –ve = d/c+d = 87/88 = 99%

positive chromosome analysis

negative chromosome analysis

New test positive 4 (a) 8 (b)

New test negative 1 (c) 87 (d)

A trial is conducted to determine which symptoms and signs have the most impact on the diagnosis of

pneumonia in patients with resp symptoms in primary care. Results are presented below:

Symptom/Sign Likelihood Ratio for diagnosis

Fever 0.94

Cough 1.00

Abnormal chest examination 1.25

Tachyponoea 1.34

Otalgia 0.07

A. Abnormal chest exam increases probability of pneumonia by 25%B. Tachypnoea has a negative association with diagnosis of pnuemoniaC. The presence of cough increases probability of pneumonia by 100%D. The presence of fever makes the diagnosis of pneumonia less likelyE. These results allow the diagnosis to be made without examining the

patient

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