Tabel 1.
Summary of Quality Measures
| Qm | Formula | Description |
|---|---|---|
| z-score based measures | ||
| Qstructure,1 | f(i,j) = (j − i) | Structural clustering |
| Qstructure,2 |  |
Structural clustering |
| Qstructure,3 | f(i,j) = 1 | Structural clustering |
| Qsurface |  |
Surface clustering |
| Qsequence | f(i,j) = δj−i,1 | Neighbors in sequence |
| non z-score based measures | ||
| Qcontrast |  |
Contact rank difference |
| QRI | TI × RE | Information content of ranks |
There are five z-score based Qm's that measure the statistical significance of the clustering among ET top-ranked residues within structure and sequence. The measures are a function of z-scores, 
where 
. The quantity w measures the top-ranked residues in contact spatially. The difference lies in the weighting term f(i,j), which weighs the contribution of residues i and j differently based on their relative position in the structure and sequence. The last two measures (Qcontrast and QRI) are unique in formula. Qcontrast is a measure of the rank gradient over the structure. QRI is structureless measure of the information content of the rank distribution. Further detail of the Qm's can be found in “Materials and Methods” section.