Screening Test Calculator — screeningcalculator • ClinicoPath

Calculates positive and negative predictive values for screening and diagnostic tests using Bayes' theorem. Demonstrates how disease probability changes with sequential testing and provides Fagan nomograms for clinical decision-making.

Usage

screeningcalculator(
  sens = 0.9,
  spec = 0.8,
  prev = 0.1,
  repeat2 = TRUE,
  repeat3 = TRUE,
  fnote = FALSE,
  fagan = FALSE,
  samplesize = FALSE,
  expected_sens = 0.85,
  expected_spec = 0.8,
  width_sens = 0.1,
  width_spec = 0.1,
  alpha_level = 0.05
)

Arguments

sens: .
spec: .
prev: .
repeat2: .
repeat3: .
fnote: .
fagan: .
samplesize: .
expected_sens: .
expected_spec: .
width_sens: .
width_spec: .
alpha_level: .

Value

A results object containing:

`results$explanatoryText`					a html
`results$mathText`					a html
`results$singleTestTable`					a table
`results$repeatTest2Table`					a table
`results$repeatTest3Table`					a table
`results$plot1`					an image
`results$plot2PP`					an image
`results$plot2NN`					an image
`results$plot3PPP`					an image
`results$plot3NNN`					an image
`results$sampleSizeTable`					a table

Tables can be converted to data frames with asDF or as.data.frame. For example:

results$singleTestTable$asDF

as.data.frame(results$singleTestTable)

Details

This calculator is particularly useful for: • Understanding screening test performance in different prevalence settings • Sequential testing scenarios (confirmatory testing) • Teaching Bayesian probability concepts in medical decision-making • Evaluating diagnostic test chains in clinical workflows