The pH values of a dye for 30 samples taken consecutively over time are listed row wise:
|
20.3
|
15.5
|
18.2
|
18.0
|
20.5
|
22.8
|
|
21.6
|
21.0
|
22.5
|
23.8
|
23.9
|
24.2
|
|
23.6
|
24.9
|
27.4
|
25.5
|
20.9
|
25.8
|
|
24.6
|
25.5
|
27.3
|
26.4
|
26.8 |
27.5 |
|
26.4
|
26.8
|
27.2
|
27.1
|
27.4
|
27.8
|
(a) Can we conclude that the sequence of pH values over time is nonrandom? Use α = 0.05.
(b) Assume that dyes are produced in batches, with 10 random samples taken from each of three batches. Explain possible special causes in the process.
(c) What type of special cause (clustering, mixture, trend, oscillation) do you suspect?
(d) What type of sampling scheme was used in this process and is it appropriate?