One thousand, seven hundred and ten personal interviews were conducted in El Prat (Barcelona) Airport involving two traditional airline companies, Iberia and British Airways, and one low-cost carrier, easyJet. All operate direct Barcelona–London flights. The fieldwork was carried out in November and December 2007. In November 298 users of Iberia were interviewed, 316 of British Airways and 318 of easyJet. In December the figures were 271 for Iberia, 264 for British Airways and 243 for easyJet.
The individuals questioned were over 18 years of age and had traveled with the airline at least three times during the previous year. This population selected because of the form of the model that requires an accumulation of experiences with the same company. According to AENAs 1,797,466 passengers flew the Barcelona–London London–Barcelona route in 2007 providing a large sample base.
To identify outliers, a cluster analysis was conducted taking the distance from the centroid as classification criterion. This allowed us to identify one homogeneous group of data and another set with atypical behavior. The study of outliers by means of the cluster technique led us to reject ten cases, three of which were users Iberia, three of users of British Airways and four of easyJet. Thus the valid sample consists of 1700 cases, with 566 interviews for Iberia, 577 for British Airways and 557 for easyJet.1