Source: Tsuriel 
The original MELD score or Model For EndStage Liver Disease score has a threedimensional distribution
It uses the following variables:
 i) Serum creatinine,
 ii) Bilirubin, and
 iii) INR (International Normalized Ratio)
The MELDNa score has a fourdimensional distribution
It uses a fourth variable if the MELD score > 11:
iv) Serum sodium
EXTRA: A MELD Score Calculator

A cstatistic gives the probability that a randomly selected patient who experienced the adverse healthcare outcome (e.g. disease, death) had a higher risk score than a patient who had not experienced this adverse healthcare outcome
∴ The cstatistic measures discrimination

We need to balance optimization (e.g. fewest number of dead patients on the waitlist) with equitybased considerations (e.g. gender, age, height, time spent on waitlist)
Beneficence and justice are two of the four principles of biomedical ethics that have been identified by Beauchamp & Childress (1979)
Questions to ponder:
Q1: Which risk factors have been omitted by the MELD score?
Q2: How do we go about assigning weights to these additional risk factors?
Q3: How do we balance optimization with equitybased considerations in our alternative measure?
Q4: Can we achieve a higher cstatistic for our alternative measure than the MELD score cstatistic?
