Delivering quality service : balancing customer perceptions and expectations / Valarie A. Zeithaml, A. Parasuraman, Leonard L. Berry. — New York : The free press, [1990]. — 226 p. ; 25 cm. — ISBN 0-02-935701-2 1. Servicios al cliente.2. Calidad. I. Parasuraman, Banu Anirudhram. II. Berry, Leonard L.. 658.89 658.562