The American Bar Association (ABA) relesaed a report that documents the public defender system in Missouri. The report used an empirical method and shows that excessive caseloads infringe on indigent criminal defendants' constitutional right to effective counsel.
The report, which can be found here, surveyed 375 lawyers in the Missouri State Public Defendant System. On average, they reported spending about nine hours on each case, while 47 hours is deemed necessary.
Other jurisdictions will be able to use this report to conduct similar workload studies for their public defender systems. This article by the ABA outlines what methods were used and gives more information about the study.