Statistics

Case control

• Risk factors
• Odds ratio
  • \(\text{Odds Ratio} = \frac{\text{Odds of cases}}{\text{Odds of controls}}\)
• Rare diseases
• Start with disease (case) and no disease (control) -> What caused this (exposure)?
• "Case-control" = "Cases Come First"
  (You start with cases, then go backward to find causes)

Cohort

• Relative risk
• Start with exposure -> What happens next (cases/disease)?
• "Cohort" = "Cause → Effect"
  (You go forward in time: Exposure → Outcome)

SD

• 1 - 68%
• 2 - 95%
• 3 - 99.7%

Formulas

• Atributable Risk (AR)
  • \(AR = \text{incidence risk in group} = \frac{ \text{a} } { \text{a} + \text{b} } \)
• Absolute relative risk reduction (ARR)
  • \(ARR = \text{AR in control group} - \text{AR in treatment group} = \frac{ \text{c} } { \text{c} + \text{d} } - \frac{ \text{a} } { \text{a} + \text{b} }\)
• Relative Risk (RR)
  • \(RR = \frac{\text{treatment incidence risk}}{\text{control incident risk}}\)
• Relative risk reduction (RRR)
  • \(RRR = \frac{\text{ARR}}{\text{control rate}}\)
  • \(RRR = 1-\text{RR} \)
• Number needed to treat (NNT)
  • \(NNT = \frac{1}{\text{ARR}}\)