1) The Institute of Transportation Studies, University of California (2001), "Background Studies on Performance Measurement for the Metropolitan Transportation Commission"
2) 佐野良夫(1996),“顧客満足の実際”,「日経文庫」日本経済新聞社
3) Derek R. Allen, Tanniru R. Rao (2000), "Analysis of Customer Satisfaction Data", American Society for Quality