I mean like the student visa has an approval rate of 60%. So, for PR applications, what is the percentage i.e. out of everyone that receives an ita, what percentage of them are approved?
There's no meaningful answer. After the ITA, the things that could result in a rejection for 'reasons' would be criminality, medical, etc. Apart from things like that, they are checking that the information is correct and truthful and corresponds to what information was used to get the ITA (education xperience language etc all are what the applicant wrote).
Student visas are completely different as there is no pre-selection process like the ITA.