Which of the statements are true about Statistical Process Control (SPC)?

a) The main task in SPC is to distinguish assignable from random variation by taking a sample of two or more observations, calculating a sample statistic (sample mean), random variations are reduced in sample statistics.

b) SPC is a statistical evaluation of the product in the production process, for which samples are taken periodically. Corrective action is taken when samples fall outside the limits.

c) It is important to remember that in SPC, random variation is a common variability of the process, and nonrandom variation is assignable variation (special variation), which can be identified (assigned to a specific cause), or can be eliminated.

d) Statistical quality control is sort of inspection that requires brainstorming, interviewing, a balance sheet, among many other financial documents, to evaluate the quality of products and to meet the expectations of the customers.

e) SPC is a technique, similar to Quality management, which became more strategic, with emphasis on customer satisfaction.