5. Control by attribute

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 C ₀ 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...