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11 Cards in this Set
- Front
- Back
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What is sensitivity?
What is the formula? |
Sensitivity = the proportion of people who have the disease (with gold standard) tested positive with the test.
Sensitivity = a/a+c |
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What is specificity?
What is the formula? |
Specificity = the proportion of healthy people tested negative with the test.
Specificity = d/b+d |
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What is Positive Predictive Value (PPV)?
What is the formula? |
PPV = the proportion of people who are tested positive with the test having the disease.
PPV = a/a+b |
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What is Negative Predictive Value (NPV)?
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NPV = the proportion of people not having the disease over the total number of people who are tested negative with the test.
NPV = d/c+d |
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Do sensitivity and specificity change with prevalence?
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Sensitivity and specificity are characteristics of diagnostic tests and do not change with prevalence.
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Applying to a condition with the prevalence of 5%. Which of the following statements are true:
a. The pre-test odds for depression is 1 in 20. b. The pre-test probability for depression is 1 in 19. c. The pre-test odds is 1 in 19. d. The pre-test probability is 1 in 20. |
a. False. b. False. c. True. d. True.
Odds is the ratio of events to non-events. A prevalence of 5% means that for every patient who suffer the disease, there are 19 non-sudderers. While probability of events to total population. For 5% prevalence, there are 1 sufferer in 20 people in total. |
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What is likelihood ratio?
What are the formulae for: Positive Likelihood Ratio Negative Likelihood Ratio |
Likelihood ratio provides a direct estimate of how much a test result will change the odds of having a disease.
LR+ = how much the odds of the disease increase when a test is positive. LR+ = sens. / 1 - spec. LR- = tells how much the odds of the disease decrease when a test is negative. LR- = 1 - sens / spec. |
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In a randomised control trial (RCT), what bias(es) of the followings are reduced by randomisation?
a) Ascertainment bias b) Selection bias c) Recall bias d) Publication bias e) Bias in handling dropouts |
Selection bias (b) is reduced by randomisation in RCT.
Ascertainment bias - bias due to non random sampling distorted by knowledge of which intervention each participant is receiving. It is minimised by blinding the researchers, clinicians and patients. |
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There are 3 types of observational studies: cohort study, case-control study and cross sectional. Describe them.
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Cohort study =
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What does it mean by:
- confounding - Bias - effect modification |
Confounding - confuses
Bias - distorts Effect modification informs |
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What are the 3 features of confounders?
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1. Has a causal association with health outcome
2. Has a statistical association with the study risk factors 3. Does not lie on the causal pathway linking the study factor and outcome. |
