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I would like to know the reliability of 20 samples. Assume there is no failure:

Reliability R(t) = ?

Confidence Level P = 80% (in every case)

Required test duration = 100 hours

Weibull paramete b = 2 (always remains 2)

I know I can use this formula: R(t) = (1 - P)^(1/(L)^b.n) where L = life time ratio

But before applying this formula I divide these 20 samples in to two groups having 10 samples each.

For first group (10 samples) I take Lifetime ratio (L) = 0.7, I apply the above formula and get R(t) = 65% (say)

For Second group (10 samples) I take Lifetime ratio (L) = 1.3, I apply the above formula and get R(t) = 70% (say)

Now I have got two reliabilities for these 2 groups. Can I combine these two reliabilities to get a final reliability? If yes, then how shall I combine these two? Shall I multiply or simple add these two?

Reliability R(t) = ?

Confidence Level P = 80% (in every case)

Required test duration = 100 hours

Weibull paramete b = 2 (always remains 2)

I know I can use this formula: R(t) = (1 - P)^(1/(L)^b.n) where L = life time ratio

But before applying this formula I divide these 20 samples in to two groups having 10 samples each.

For first group (10 samples) I take Lifetime ratio (L) = 0.7, I apply the above formula and get R(t) = 65% (say)

For Second group (10 samples) I take Lifetime ratio (L) = 1.3, I apply the above formula and get R(t) = 70% (say)

Now I have got two reliabilities for these 2 groups. Can I combine these two reliabilities to get a final reliability? If yes, then how shall I combine these two? Shall I multiply or simple add these two?

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