SPC Simplified for services: Practical tools for continous quality improvement / Davida M. Amsden, Howard E. Butler, Robert T. Amsden. — Nueva York : Quality Resources, [1991]. — 299 p. ; 23 cm. — ISBN 0-527-91639-0 1. Calidad.2. Métodos estadísticos. I. Butler, Howard E.. II. Amsden, Robert T.. 658.562:519.2