Brady Shared "Statistics" - 17 Picmonics
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Statistics
Cohort Study
- Observational
- Longitudinal
- Studies risk from exposure
- Retrospective
- (Asks) "Who developed disease?"
- Prospective
- (Asks) "Who will develop disease?"
1 min
Case Control Study
- Observational
- Retrospective
- Compares those with disease to those without
- (Asks) "What happened?"
- Measurement
- Odds Ratio
47 secs
Cross-Sectional Study
- Observational
- (Asks) "What's Happening?"
- Data at One Specific Point in Time
- (Finds) Frequency of Disease
- Measurement
- Prevalence
49 secs
Quantifying Risk: Contingency 2x2 Table Setup
- Disease
- Along Top (x axis)
- Exposure
- Along Side (y axis)
- A: Exposed and Diseased (Sick)
- B: Exposed and Healthy
- C: Not Exposed and Diseased (Sick)
- D: Not Exposed and Healthy
2 mins
Sensitivity
- Characteristics
- Rules Out
- Screening Test
- Formula
- TP / (FN+TP)
2 mins
Specificity
- Characteristics
- Rules In
- Confirmatory Test
- Formula
- TN / (TN + FP)
1 min
Positive Predictive Value (PPV)
- Proportion of Positive Tests that are True Positive
- Probability that Person with Positive Test has Disease
- Formula
- TP (True Positives)
- Divided by /
- All Positive Test Results
- TP + FP
- Considerations
- Varies Directly with Prevalence
1 min
Negative Predictive Value (NPV)
- Proportion of Negative Tests that are Truly Negative
- Probability that Person with Negative Test is Healthy
- Formula
- (TN) True Negatives
- Divided by /
- All Negative Test Results
- (FN + TN)
- Considerations
- Varies Inversely with Prevalence
1 min
Odds Ratio (OR)
- Use
- Case Control Studies
- Measures Association Between an Exposure and an Outcome
- Formula
- Odds of Exposure in Diseased (Sick) Group
- a / c
- Divided /
- Odds of Exposure in Healthy Group
- b / d
- Interpretation
- =1 Exposure does not affect odds
- > 1 Exposure increases disease
- < 1 Exposure decreases disease
2 mins
Relative Risk (RR)
- Use
- Used in Cohort Studies
- Formula
- Risk of Developing Disease
- Equals =
- Exposed Group
- a / (a + b)
- Divided by /
- Unexposed Group
- c / (c + d)
- When Low Prevalence Odds Ratio Approximates Relative Risk
2 mins
Attributable Risk (AR)
- Use
- Proportion Exposure Increases Disease
- Formula
- Incidence of Diseased (Sick)
- Equals =
- Exposed Group
- a / (a + b)
- Minus -
- Unexposed Group
- c / (c + d)
1 min
Relative Risk Reduction
- (risk in unexposed - risk in exposed) / risk in unexposed
- Formula
- Treatment effects
- RRR = 1 - RR
Absolute risk reduction (ARR)
- Effect of Treatment
- Formula
- Control Event Rate - Experimental Event Rate
- NPV - PPV
- ARR = (c/(c+d)) - (a/(a+b))
Attributable Risk Percent (ARP)
- Meaning
- % of disease caused by exposure
- Formula
- (Risk in exposed - Risk in unexposed) / Risk in exposed
- (Relative Risk - 1) / Relative Risk
Likelihood Ratio
- Meaning
- Probablity that person does or doesn't have the disease
- Formula
- LR+ = Sensitivity / (1- specificity )
- LR- = (1- Sensitivity) / Specificity
- Interpretation
- LR >1
- LR = 1
- LR < 1
Likelihood ratio (DELETED)
- All Positive Test Results
- Sensitivity / (1- Specificity)
- All Negative Test Results
- (1- sensitivity) / Specificity
Number needed to treat or harm
- Number needed to treat
- Number needed to treat
- 1/ control event rate - experimental event rate
- Number needed to harm
- Number needed to harm
- 1 / experimental event rate - control event rate
