[modeller_usage] z-DOPE score

Hi,

I have a question regarding the zDOPE score. I have read some paper that state this: "The Z-DOPE scores ranged from −1.63 to −1.85, where a score of less than −1 indicates a “reliable” model (i.e., 80% of its Cα atoms are within 3.5 Å of their correct positions)"

I am wondering how is it that a score of less than -1 indicates that 80% of its Cα atoms are within 3.5 Å of their correct positions? How is it possible to know the percent of atoms in the "correct position" based on how small (or not) the z-DOPE is?

What can I say about the magnitude of the negative values besides stating that since the models have negative values they are acceptable?

Best,

Mariana