I missed the reference to physics before.
AIP data and publications pertain to physics departments specifically.
For example:
rosters:
https://www.aip.org/sites/default/files/statistics/rosters/physrost16.4.pdf
“Physics bachelor’s receiving their degrees from departments that
grant graduate-level physics degrees are more likely to pursue
graduate study in physics.”
http://www.aip.org/statistics/trends/reports/bach2010.pdf
“•Physics bachelors from large departments are more likely to attend graduate or professional school with the intention of earning a degree in any field than physics bachelors from smaller departments (Figure 1).
•Graduates of large departments rate their physics and math preparation for a career more highly than graduates of smaller departments”
“http://www.aip.org/statistics/trends/highlite/bachplus5c/bachplus5c.htm”
"