Public Health

Question 1

Best type of study for therapy?

Answer 1

Randomised controlled trial RCT > cohort

Question 2

Best type of study for diagnosis?

Answer 2

Prospective, blind comparison to a gold standard

Question 3

Best type of study for etiology/harm?

Answer 3

RCT > cohort

Question 4

Best type of study for prognosis?

Answer 4

Cohort > case control

Question 5

Best type of study for prevention?

Answer 5

RCT > cohort study

Question 6

Best type of study for clinical exam?

Answer 6

Prospective, blind comparison to gold standard

Question 7

Name the 4 phases of diagnostic research

Answer 7

• Phase 1: compare test results of target disorder and normal people (ideal circumstances)
• phase 2: sensitivity and specificity
• phase 3: if suspect target disorder, does test distinguish Those with and without (usual circumstances)
• phase 4: does diagnostic test better prognosis

Question 8

How calculate positive predictive value

Answer 8

Positive disease / positive test

Question 9

How calculate negative predictive value

Answer 9

Negative disease / negative test

Question 10

How calculate study prevalence

Answer 10

Patients with target disease / total patients

Question 11

How calculate sensitivity

Answer 11

Positive test / positive disease
SnOUT

Question 12

How calculate specificity

Answer 12

Negative test / negative disease
Rule in spIN

Question 13

Define pre test probability

Answer 13

The background prevalence in group of people you’re testing

Question 14

How calculate likelihood ratio

Answer 14

(Positive test/positive disease) / (positive test / negative disease)
= sensitivity/ (1-specificity),

Useful because post test odds of having disease = pretest odds of disease x Lr

Question 15

What is a fagan monogram and what is needed

Answer 15

Graphical tool for estimating how much the result on a diagnostic test changes the probability that a patient has a disease. For this, you need the pre-test probability and the likelihood ratio

Question 16

How is study validity determined (8)

Answer 16

Primary guides
• Assignment of patients to treatments * randomized * and randomization concealed
• all patients properly *accounted for and attributed *
• * follow up * complete
• *Intention to treat analysis *: patients analyzed in the groups to which they were randomised

Secondary guides
• were all involved blind to treatment
• were groups * similar * at start of trial
• were groups * treated equally *
• is * sample size * determined prior to avoid type 2 error, and numbers reached?

Validity = truthful, free of bias (systematic error)

Question 17

Which 2 forms of error in research must be excluded to prove validity

Answer 17

• Random error (chance, p values)
• systematic error (bias)

Question 18

How calculate relative risk

Answer 18

risk of negative outcome on target drug / risk on placebo
(Risk ratio in % )

Question 19

How calculate absolute risk

Answer 19

Risk of negative outcome on placebo - risk on target drug
Eg 10% -5% = absolute risk is reduced by 5% (5 less patients out of 100 will get disease)

Question 20

How calculate number needed to treat NNT

Answer 20

NNT to get 1 less negative outcome/disease = 100 / absolute risk
Eg if absolute risk is reduced by 5%, need to treat 20 patients so that 1 less patient suffers the negative outcome eg stroke

Give better idea about clinical significance

Question 21

Define statistically significant (2)

Answer 21

P < 0,05

95% Confidence interval cannot contain 1

Question 22

How interpret rr 0,5 (95% CI 0,2 - 0,7)

Answer 22

I am 95% confident that if I use this target drug in the population of people with this disease then the rr will be between 0,2 - 0,7 so the relative risk reduction will be between 30 and 80%

0,5 = sample results (study result)

1 is not in the 95% CI therefore statistically significant

Question 23

Define clinically significant

Answer 23

RRR (relative risk reduction) 25% or more
But use mostly absolute risk reduction and NNT to decide

Question 24

What tells us about precision in a study?

Answer 24

Confidence intervals

Question 25

How express uncertainty in meta-analysis

Answer 25

Or = 1
0 (treatment better ) or ( 1 ) - 2 (treatment worse)