Question: In a u charting context, the number of standard units inspected may vary from period to period. Let
(a) From these values, what conclusions can you make about stability of the process being monitored? Make the appropriate control chart.
(b) Suppose that in the future will be held constant at 1 and that 2.4 nonconformances per inspection unit will be considered to be "standard quality." Find the probability of an out-of-control signal on a 3-sigma Shewhart control chart, if the true nonconformance rate is at the standard quality level (λ = 2.4). Find the probability of an out-of control signal if the true nonconformance rate changes to λ = 4.8. (Remember that the Poisson(μ) probability function is P(X = x) = (exp (-μ) μx) /x! .)
(c) Suppose that in the future ki will be held constant at 2. Find the probability of an out-of-control signal if the true nonconformance rate is at the standard quality level (λ = 2.4). Find the probability of an out of-control signal if the true nonconformance rate changes to λ = 4.8
(d) Compare your answers to (b) and (c). Which subgroup size (k = 1 or k = 2) is more appealing? Why?