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What do the R & C in RCT mean? Randomised – equal chance of receiving
treatment
Control – there is a control group to which the new treatment is compared
What is PICO and what is it used for? What am I for?A well built study question
Patient problem/populationInterventionComparisonOutcomes
Know Be able to identify different types of
study Bradford hill criteria
3 types of bias Selection Information Confounding
Odds
Odds any given day is a Tuesday?=1/6
The Odds Ratio (OR) in the analysis of case-control studies
Cases(diseased)
Controls(non-diseased)
Exposed a b
Unexposed c d
bc
ad
bc
da
d
b
c
aOR
The Odds Ratio (OR) in the analysis of case-control studies
Controls(non diseased)
Cases(diseased)
Exposed a b
Unexposed c d
ad
cb
c
a
d
bOR
The IRR in cohort studies
Cases(diseased)
Controls(non-
diseased)Total
Exposed a b a+b
Unexposed c d c+d
d)(c
c
b)(a
aIRR
What can’t you use IRR in case control studies? You choose the number of controls
Odds Ratio (OR) vs Incidence Rate Ratio(IRR)
Looking back on his first year, ???? decides its time to visit the Gum clinic. Shocked by an unwanted resulted he decides it was in fact not his fault but just a product of the fact he was hanging out so much with Fresher's on main campus. In an effort to justify himself he wants to know if there is any evidence for his belief that it is regularly hanging out with Fresher’s on main campus that was in fact the problem. 150 of his course mates kindly offer to allow him to check all their medical records (in the name of science of course) and gets them to fill in detailed information about with whom they have been socialising.
He finds that of his 150 course mates only 30 of them have been gallivanting on a regularly basis with muggle freshers, 15 of whom unfortunately have the clap. Of those that ‘kept it in the family’ 30 were unfortunate enough to be infected
Is this a good study?
Calculate the OR and IRR please
Odds Ratio (OR) vs IRR Common Disease
Cases(diseased)
Controls(non-diseased)
Exposed 15 15 30
Unexposed 30 90 120
33015
9015OR
2120/30
30/15IRR
Cases(diseased)
Controls(non-
diseased)
Exposed 15 15 30
Unexposed 30 90 120
Square root of (1.78) = 1.33Exp(1.33) = 5.98
Standardised mortality ratioSMR
= Observed deaths / expected deaths x100
Standardised mortality ratio In a US study 300000 of gangsta
rapsters 60 were found to have been murdered. The Us homicide rate is 5 per 100000.
What is the Standardised mortality ratio?
SMR = 20/5 x100 = 400
How many times more likely were gangstas to be murdered? 4
Sensitivity = test’s ability to identify a condition correctly
Specificity = test’s ability to exclude a condition correctly
Sensitivity = 51/59 = 86.4% Specificity = 30/62 = 48.4%
Positive predictive value = the likelihood that someone with a positive test result actually has the disease.
Negative predictive value = the probability that subjects with a negative screening test truly don't have the disease.
PPV = 51/83 = 61.4% NPV = 30/38 = 78.9%
3 things for a trial to be ethical - Clinical equipoise i.e. is there reasonable uncertainty
about which is the best type of treatment, if not it is not ethical to carry out the study
- Ethical dilemma - Clinician should provide best treatment for each individual patient. Scientific integrity requires treatment chosen randomly. GOOD STUDY DESIGS
- Is informed consent being taken i.e. does the patient know that they will be randomised (i.e. ‘informed’), and has given written consent ?
Informed consent for trialwhat the alternative treatments are
(including known side effects)– that treatment will be allocated at random– that patients may withdraw at any time
Information should be given – verbally and in writing with ‘cooling off’ time– by a knowledgeable informant
