This book differs from the ordinary textbooks on statistics. It aims to show how to apply the methods of statistics to the real world problems. People often try to reduce defects by tracing directly back to the cause of the defect. Though this approach may seem to be efficient at first glance, the cause obtained in most cases are not the true causes. If remedies are based on this knowledge, the attempt may be abortive, the effort wasted. The first step in finding true cause is careful observation of the phenomenon when true cause becomes apparent. Statistical tools lend objectivity and accuracy to observation. The maxim of statistical way of thinking are: “Give greater importance to facts than abstract concepts.” “Do not express facts in terms of senses or ideas. Use figures derived from specific observational results.” “Observational results, accompanied as they are by error and variation, are part of a hidden whole. Finding that hidden whole is observation’s ultimate goal.” “Accept regular tendency which appears in a large number of observational results as reliable information.” One must first thoroughly understand imperfection of human recognition. One must then understand that knowledge presently held in nothing more than grounds for further hypotheses. After gaining that understanding, the above-mentioned methods of thinking can be used to further deepen our understanding of the production process and the ways to improve it.