For whatever it's worth, I ran some statistics on some numbers from AFPC's static stats site (under "RAW" on the AFPC secure apps site).
My nerdery is attached.
I reckoned if the AF values pilots (or some other field) over another, then that field will have a higher representation in the "Select" pool as compared to its proportion of the "Considered" pool for a promotion board.
For example, in the 2017 Lt Col Board, 30.3% of those considered were pilots, while 31.39% of those selected were pilots. 31.48% of those considered were mission support, while 32.82% selected were. So, pilots and mission support ended up with a bigger piece of the pie than CSO, ABM, and non-rated ops. Theoretically, that would mean the AF values those fields more.
What I found was, using a statistical test of significance (Z value), there isn't a significant over/under representation over the past 5 years among pilots, CSOs, ABMs, non-rated ops, and mission support for the IPZ board to Lt Col. However, for BPZ to Lt Col, and in BPZ and IPZ to Col, pilots make up a larger share, both historically and over the past 5 years.
What I think this indicates is that your IPZ rates are based on steady state staff and squadron command opportunities within each community. But, the high representation of pilots in the BPZ pool shows that the AF is ensuring its HPOs and future GOs will be pilots. I don't have data to show if those making BPZ are the best pilots/officers/leaders, or whatever; just that the AF values pilots as senior leaders.
Not sure I'll affect anyone's opinions, but I thought I'd share. Also, I don't think I have to ask, but please point out any errors I've made in the analysis.
Hist LAF Stats.xlsx
LAF Promotions Proportion Study.pdf