H1B Visa Analysis

As an international student in the United States, I wanted to research more about numbers behind the H1B Visa process. The current administration in Washington emphasized that the system has recently been "abused" and I wanted to focus on quantifying such a claim. I tried to address three questions:

1. Do certain firms petition for the H1B Visa much more than other companies do?
2. Do employers at such firms underpay their employees (enough to drive Americans out of jobs)?
3. How important is the H1B Visa to the business model of such firms (as measured by stock performance)?