Question

the basic logic of statistics and probability of control schemes

Answer 1

Statistics is purely based on scientific data analysis with aim to interpret the relevant information about the population using this sample data. In quality control Sampling and Probability technique is used to check quality status. In control chart we usually use 3 sigma control limits. The logic behind this is, 99.73% of data points are within the 3 Standard deviation for a Normal population. So we assuming the data is Normally distributed then using that property we can infer that quality characteristics ( process average ) must be with in 3 sigma control limits will assures quality of the manufactured product.