Quote by Kaoru Ishikawa

When you see data, doubt [them]! When you see measurements, doubt them!


quoted in Gemba Kazien by Masaaki Imai. His text after the quote: "He knew that many data are collected in the company to please the boss and that measurements are often made or recorded incorrectly by devices. At best, measurements are only secondary information that does not always reflect the actual conditions."

Please suggest source details if you know: book, page, year, online article address (url), correction (different author...), etc.. Thanks.