Shōwa 25-nen kokusei chōsayō shokugyō bunrui to Shōwa 15-nen kokusei chōsa shokumeihyō : 1950-nen Beikoku jinkō sensasu shokugyō bunrui, kokusai hyōjun shokugyō bunrui hikakuhyō (Tōkei Iinkai Jimukyoku, 1951)