Table 3 CUSUM and SPRT calculations, according to Davies et al [26].

p₁ is the unacceptable failure rate (set at 0.3)

α is the type 1 error (set at 0.05)

β is the type 2 error (set at 0.2)

The CUSUM is increased by 1 - s for a failure and decreased by s for a success.

a = ln [(1 - β)/α] = 2.773

b = ln [(1 - α)/β] = 1.558

P = ln(p₁/p₀) = 0.693

Q = ln [(1 - p₀)/(1 - p₁)] = 0.194

s = Q/(P + Q) = 0.219

h₀, the lower boundary limit, = -b/(P + Q) = -1.756

h₁, the upper boundary limit, = a/(P + Q) = 3.126