The quality engineer uses PDCA (Plan-Do-Check-Act). The plan phase consists of looking into the customer complaint data and using stratification to separate the complaint characteristics; a run chart is created. The run chart indicates that there are more complaints for smaller-diameter parts with rust than larger-diameter parts. The quality engineer uses deduction to hypothesize that more small-diameter parts were sold, and that is the reason for the higher number of complaints. The do phase consists of a quick check of completed work orders for the past year; these indicate the quantities are approximately the same. The check of the work orders results in rejecting the hypothesis and forming a new hypothesis.