Formulae for MRCPsych

  1. Sensitivity
    A/(A+C)x100
  2. Specificity
    D/(D+B)x100
  3. Likelihood ratio for a positive test - definition
    LR shows how much more likely someone is to get a positive test if he/she has the disease, compared with a person without disease.

    Positive LR is usually a number greater than one and the negative LR ratio usually is smaller than one.
  4. Likelihood ratio for a negative test - definition
  5. Likelihood ratio for a positive test - formula
    Sensitivity/(1-Specificity)
  6. Likelihood ratio for a negative test  - formula
    (1-Sensitvity)/Specificity
  7. Negative predictive value - definition
    The proportion of patients with negative test who are actually free of the disease.

    This refers to the proportion of those scoring negative that don't have a condition (i.e. The chance that a negative result will be correct).

    Inversely proportional to prevalence.
  8. Negative predictive value - formula
    D/(D+C)x100
  9. Positive predictive value - formula
    A/(A+B)x100
  10. Positive predictive value - definition
    The proportion of patients with positive test who actually have the disease.

    Affected by prevalence - directly proportional.
  11. Pre-test probability
    (a+c)/(Total)
  12. Pre-test odds
    Pre-test probability/(1-pre-test probability)
  13. Post-test odds
    Pre-test odds x likelihood ratio for a positive result
  14. Accuracy
    (A+D)/Total
  15. Absolute risk reduction
    CER - EER
  16. Relative risk
    EER/CER
  17. Absolute risk reduction
    CER - EER
  18. Number needed to treat
    1/ARR
  19. Standard error of the mean
    Standard deviation/√sample size
  20. Attributable risk proportion
    = AR/EER

    or (A/A+B) - (C/(C+D))
  21. % results within 2 SD of mean?
    95.4%
  22. Relative risk reduction
    (CER - EER)/CER
  23. Standard deviation
    √variance
Author
Em262
ID
339307
Card Set
Formulae for MRCPsych
Description
Formulae to know for MRCPsych Paper B
Updated