Bio Stats

Question 1

• Incidence?

- Prevalence?

Answer 1

• new cases / people at risk

- existing cases / populatio

Question 2

• RR?
• OR?
• AR?
• NNT?

Answer 2

4x4: D H on top and E NE on side: AB
CD
RR= A/A+B / C/ C+D or Rate among exp/RANE
OR= A/B / C/D
Rate among exposed - R among unexposed
- 1/AR

Question 3

• Sensitivity? Detects what? Effect of prev.?

- Specificity? Detects what? Effect of prev.?

Answer 3

• TP/TP+FN ; Disease when actually there
• TN/ TN+FP ; Absense of disease when not there
• No

Question 4

• PPV? Means? Increases with?
• NPV? Mean? Increases with?
• Increased spec does what?
• Increased sensitivity does what?
• What happens with rare disease?

Answer 4

• PPV: TP/TP+FP; + test actually has disease; high prevalence
• NPV: TN / TN+FN; - test are actually disease free; low prevalence
• Increases PPV
• Increases NPV
• ## More FP’s than TP’s

Question 5

• Lead time bias?

- Length time bias?

Answer 5

• Screening picks up illness earlier

- Screening picks up people with increased asymptomatic phases