Ok, I've seen this statement quite often from all these worker unions. Can someone point me to a source showing: 1.what fraction of the job market H1B workers

Ok, I've seen this statement quite often from all these worker unions. Can someone point me to a source showing: 1.what fraction of the job market H1B workers took away? 2.among these jobs taken, how many were taken by H1B workers that are brought in directly from other countries? 3.how many are people who went through college/master/PhD eduction in the US and followed the rules and got H1B? It must not be hard for DHS to gather these stats, right? It would be a lot easier to counter arguments/come up with strategies using these statistics.