VLAD Chart (Variable Life-Adjusted Display) calculator
Plot a variable life-adjusted display online. Track cumulative lives saved or lost against a risk model's prediction, case by case, with optional risk adjustment fitted in the chart.
What it does
Plots the running total of lives saved or lost against what a risk model predicted, case by case. The line rises when outcomes beat prediction and falls when they fall short.
When to use it
You are monitoring one unit's binary outcomes over time and want a picture of cumulative performance that already accounts for case mix.
Alternatives
- CUSUM for a pass/fail outcome — you need a formal signal with a controlled false-alarm rate, rather than a running picture
- Funnel — you are comparing several units at one point in time rather than one unit over time
How to read the output
- Read the SLOPE, not the level
- The y-axis is a cumulative difference, so it carries the whole history. A line sitting well below zero may have been flat — and therefore performing exactly as predicted — for the last two years. The current level records the past; only the slope describes the present. This is the single commonest misreading of a VLAD.
- It is only as good as the risk model
- Every point is an observed outcome minus a predicted risk. A model that under-predicts risk for this unit's patients will make a competent unit look poor, and vice versa. A model fitted to the very cases being monitored reproduces their total exactly and flattens the chart by construction — the predictions must come from elsewhere.
- What it cannot separate
- A downturn is a prompt to investigate, never a conclusion. A run of genuinely worse care, a run of bad luck, and a shift in case mix the model does not capture all look identical here.
How this calculator is validated · Which statistical test should I use?