Basically 500 individuals were considered as sufficient to represent the national sample. The total sample size of 600 was reached considering the interviews completed during the pilot phase and the additional individuals for oversampling frequent car users. The sample size of 600 individuals for each country was chosen according to the budget available for the study. When a sample survey is organized for estimating a specific variable (. the proportion of population holding a certain preference) the definition of the sample size can be based on the desired confidence interval for the estimator. This survey was aimed at collecting a.
