Control by attribute
Statistical observation

An important special case, from a technical or commercial point of view, of statistical observation is when its sole purpose is to classify objects into categories, such as "satisfactory" or "defective". Such classification presupposes a rigorous definition of each category. For an electric motor where motor torque is considered the discriminating parameter, the motor will be classified as satisfactory when torque C is greater than the specified value C ₀. It doesn't matter that the engineer has taken care to specify this C₀ value with a safety margin in relation to the actual torque C_R which is sufficient to operate the machine. If C _R < C 0 , the motor will have to be classified as faulty! We find the same type of remark when we consider the definitions of reliability or quality. Engineers must not confuse their rigorous attitude to statistical...