Questions about phrases of a study!

I am currently writing a study, and have a question about those sentences...Is this correct, or how would it be better?

XYZ can occur after severe YZX. Its incidence had been reported in the literature ranging from 0.5 - 45%. This variety could be due to incorrect diagnosis regarding patients who developed a XXX. Furthermore, the varying incidences could be explained by inconclusive international diagnostic criteria.

and

The results by international studies dealing with the predictive risk factors that could lead to a XXX remain inconclusive.

Thank you very much!