What is the visa approval ratio for Italy, or for my university?

Short answer: I do not know, and it is the wrong question. Each application is decided on its own documents.

Why the question feels urgent

If there were a ratio, there would be a better queue to join, and the outcome would be about picking rather than preparing. That is a comforting thought when you are anxious and the process is long.

Why it does not work that way

• A refusal is a reasoned decision about one applicant's file (Ministry of Foreign Affairs). It is not a quota being filled or emptied.
• The one published constraint on numbers is not a visa ratio. Universities may validate pre enrolments only up to their places for non EU students plus 20% (MUR circular). That is a cap on pre enrolments, applied by the university, before any visa is in the picture.
• Your file's weak points do not improve by choosing a different university, and your strong points do not weaken by choosing a popular one.

What the circulating numbers usually are

One of three things. A figure for short stay Schengen tourist visas, which is a different visa under different rules. An agency's own success rate, which is a sales figure about a self selected group of clients. Or a number with no source at all, repeated until it sounds official.

What to do instead

Spend the hours on the four published rules in V14. Those are the parts of this process that answer to effort.