Stats

Sensitivity and Specificity

  • Sensitivity: true positives/all patients with disease
    • SnNout: with high sensitivity, a negative test rules diagnosis out
  • Specificity: true negatives/all patients without the disease
    • SpPin: with high specificity, a positive test rules diagnosis in

Positive and Negative Predictive Value

  • Positive Predictive Value: true positive/all positives
  • Negative Predictive Value: true negatives/all negatives

Likelihood Ratio (LR)

  • Likelihood Ratio (LR): odds of a positive test in patients with the disorder compared with those without the disorder = sensitivity / (1 -specificity)

Incidence and Prevalence

  • Incidence: number of new cases occurring in a population over a given period of time (month, year, etc)
  • Prevalence: number of current cases per population (example: number of cases per 10,000 people)
    • Point Prevalence: proportion of a population that has the condition at a specific point in time
    • Period Prevalence: proportion of a population that has the condition at some time during a given period (example: 12-month prevalence), and includes people who already have the condition at the start of the study period as well as those who acquire it during that period
      -Lifetime Prevalence: proportion of a population that at some point in their life (up to the time of assessment) have experienced the condition

Risk Reduction

Example Data Set from National Lung Screening Research Trial [MEDLINE]

  • Mortality Rate from Lung Cancer
    • Radiography: 309 deaths per 26,732 participants
    • Low-Dose CT: 247 deaths per 26,722 participants
      • Relative Risk Reduction (as Compared to Radiography): (309-247)/309 = 20% relative risk reduction
      • Absolute Risk Reduction (as Compared to Radiography): 309/26,732 – 247/26,722 = 1.16% – 0.92% = 0.24% absolute risk reduction

References

  • National Lung Screening Research Trial Team: Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med 2011;365:395-409 [MEDLINE]