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Mafs

Mafs. Gareth g.k.knott@warwick.ac.uk. 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

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Mafs

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  1. Mafs Gareth g.k.knott@warwick.ac.uk

  2. 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

  3. What is PICO and what is it used for? • What am I for? A well built study question Patient problem/population Intervention Comparison Outcomes

  4. Know • Be able to identify different types of study • Bradford hill criteria

  5. 3 types of bias • Selection • Information • Confounding

  6. Odds Odds any given day is a Tuesday? =1/6

  7. The Odds Ratio (OR) in the analysis of case-control studies

  8. The Odds Ratio (OR) in the analysis of case-control studies

  9. The IRR in cohort studies

  10. What can’t you use IRR in case control studies? • You choose the number of controls

  11. 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 mugglefreshers, 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

  12. Odds Ratio (OR) vs IRR Common Disease

  13. Square root of (1.78) = 1.33 Exp(1.33) = 5.98

  14. Standardised mortality ratio SMR = Observed deaths / expected deaths x100

  15. 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?

  16. SMR = 20/5 x100 = 400 How many times more likely were gangstas to be murdered? 4

  17. Sensitivity = test’s ability to identify a condition correctly • Specificity = test’s ability to exclude a condition correctly

  18. Sensitivity = 51/59 = 86.4% • Specificity = 30/62 = 48.4%

  19. 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.

  20. PPV = 51/83 = 61.4% • NPV = 30/38 = 78.9%

  21. 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 ?

  22. Informed consent for trial what 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

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