Agreed these sort of comparison needs normalization but it also needs to normalize the average years of service when comparing attrition rates.....mig-21 crash can't be compared to f-16 block 4 crash for instance...to get reasonable precision requires a bit more formal stats analysisAircraft crashes are measured per flight hour or number of flights/sorties. Its makes no sense to compare absolute number of crashes between the Indian Air Force which has about 1,200 aircraft with the USAF which has more than 5,500 aircraft (they have more than 1,200 F-16s alone !)
Also those UH-60 chopper crashes don't come in this 5,500 aircraft because they were from the Army National Guard not USAF.
The Indian Air Force has lost 3 Mig-21 Bisons in just 5 months out of roughly 80 in service, which works
out to an annual attrition rate of almost 10% a year!