还是得请大家帮忙确认下，搞得头晕！

Bellcore里：FailureRate=(10^9*N*r)/Ttotal;
Nisthenumberofrandomfailures,
TtotisthetotaldevicehourscalculatedfromtheArrheniusrelationship,and
ristakenfromχ2(α,,2N+2).

MIL338里面MTBF=2T/χ2(α,,2N+2)
T=TotalPowerOnTime,N=TotalFailurenumber;
α=1−confidence=1−0.9

请问以上两个哪个是对的？Bellcore里多了个失效数N，而338里直接除以χ2(α,,2N+2)，比Bellcore少了N，找了好多资料都没人提及这是怎么回事，请教大家了，谢谢！