The postal survey was addressed to the person responsible for the environment or logistics in the firm. All the surveys returned were reviewed, and in the case of a defect in the filling out of any of these being found, the company was contacted by telephone in order to rectify the error before being included in the tables. The SPSS software package
was employed to carry out the statistical analyses.
One difficulty found in the field study was the prior lack of knowledge with respect to whether the firms used glass containers or not in the bottling or packaging of their products. For this reason, the accompanying letter of presentation requested the firms who did not use glass containers to also return the questionnaire, explaining their motives for
choosing other types of containers. The goal here was to estimate the percentage of firms in the initial population that did not use glass containers for their products, since these were not the object of the study. The results obtained show that 27.7% of Spanish firms in the sample never used glass containers in any case whatsoever (they prefer containers made of a different material, plastic or metal for example) to place their products on the market. In the Belgian case, in contrast, this percentage rose to 76.1%.