Interactive calculators
Interactive tools for medical biostatistics: drag the inputs and watch the output move. Each one turns a formula you would otherwise have to trust into a picture you can see.
PPV / NPV calculator
Predictive values · prevalence · the 2×2
Drag prevalence, sensitivity and specificity, and watch why a 99%-accurate test can still be wrong most of the time — with the 2×2 table and 1,000 patients on screen.
NNT calculator
Relative vs absolute risk · RRR · ARR · NNT
Set the control and treatment risk and see RRR, ARR, NNT and the odds ratio on 100 patients — and how the same trial can be spun three different ways.
ROC curve & threshold
Sensitivity–specificity trade-off · AUC
Move one decision threshold and watch sensitivity and specificity trade off as the point traces the ROC curve and AUC scores the test.
Kaplan-Meier curve
Survival · censoring · median
Build the survival curve by hand: every step is an event, every tick a censored patient. Drag ten patients around and watch the curve redraw.
Screening bias
Lead-time bias · length bias · overdiagnosis
Why earlier detection can look like longer survival even when nothing about the disease has changed: lead-time and length bias, made visible.
Fagan nomogram
Pre-test to post-test · likelihood ratios · Bayes
Set the pre-test probability and the likelihood ratio, and read the post-test probability off the third axis. The straight line is Bayes' theorem, drawn in log-odds.