My hypothesis correlates size of law firm with average shortness of legal careers. The larger the law firm, the lower the average number of years out of law school of its lawyers. If you hire a 1,000 lawyer firm, all the associates on the matter and the relatively diminished input of the partner drops the average experience level. On the other end, if you hire a small firm, it is likely that a seasoned partner does a large part of the work. Large matters that require leverage should show such a “demographic” decline.
It would not be hard for a large law department to gather data that confirms or contradicts this hypothesis. A group of law departments could pool their data. The next step would be to test the correlation between average legal experience and cost or results. It would not surprise me if the average invoice size rises while the average biller experience drops.