Ultimate Loss-IBNR

In some IBNR valuation, Actuaries derive their ultimate loss form combination of several reserving methods(chain Ladder, BF, Frequency-severity ). As example : Ultimate Loss= 20%ChainLadder + 50%BF + 30%F-S like this .

So, how we interpret this and what are the reasons for that???



Thanks

Ultimate Loss-IBNR