I too would advise that anyone looking into this makes as much use of context as possible at the time BMH's were few and far between and served a much larger catchment area then a local hospital did.
I wouldn't be surprised if the mortality rate in every age band showed abnormalities when compared to a similar civilian establishment just due to the fact that that's where all MOD personnel ended up. Both my sisters were born in Rinteln despite my dad being stationed in two different locations many miles apart and much further from Rinteln then would expected in a civilian location.
my daughter was born in 1996 she was very early and very small and a nurse of many years experience told us that we were lucky as maybe even just 5-6 years before she would probably have been unviable purely because the levels of care and treatment that saved her were just not around
It's not the case that all MOD personnel and families were treated in military hospitals. Many were treated in German hospitals, usually as emergencies, and these were often the most seriously ill and injured. German ambulance services rarely took patients to BMH or RAF hospitals - in 4 years at Wegberg I can only recall one occasion, and that was because the incident occurred <0.5k away, and the patient was moribund. I also recall collecting quite a number of bodies from hospitals in Germany, Belgium and the Netherlands (usually, but not always, RTCs).
Local policy would have had an impact. The RAF regularly took emergency patients to local hospitals (they could be transferred once stable), whilst the Army often transported patients long distances in elderly ambulances.
Some patients were transferred from British hospitals to German facilities for specialist treatment. I took patients from Wegberg to Aachen (Burns Centre and Neurosurgery) and Duisburg (decompression chamber), for example.
Also, some seriously ill patients were aeromedically evacuated to UK, so if they subsequently died they wouldn't appear in BFG mortality data.
It would be interesting to compare mortality rates, because it always seemed as if BFG had a particularly high number of deaths from RTCs and suicide, but I'm not sure if the data is available.