How to explain the ΔΔG?

I try to use the FOLDX. But when I analysed the result, I got confused. (1)Others think that if ΔΔG>0 then destabilize otherwise stablize. I run the program, and ΔΔG=-4.14kcal/mol. Can I think that it stabilize significantly? And I used other predictors,such as I-Mutant 3.0 or i-Stability, the results of ΔΔG<0, and showed it destabilize. If the standard of judge is differrent, in other word, the meaning of "-/+" is different? (2)What is the threshold? 0.5kcal/mol or 1kal/mol?

DDG sign is only a convention, according to thermodynamics a negative DDG implies that your system releases energy achieving a more stable state.