17.16 More on the tablet compression process.

Exercise 17.15 concerns process control data on the hardness of tablets for a pharmaceutical product. Table 17.5 gives data for 20 new samples of size 4, with the x and s for each sample. The process has been in control with mean at the target value μ = 11.5 and standard deviation σ = 0.2.

(a) Make both x and s charts for these data based on the information given about the process.

(b) At some point, the within-sample process variation increased from σ = 0.2 to σ = 0.4. About where in the 20 samples did this happen? What is the effect on the s chart? On the x chart?

(c) At that same point, the process mean changed from μ = 11.5 to μ = 11.7. What is the effect of this change on the s chart? On the x chart?