This paper presents a method to account for response behavior heterogeneity in the quantification of adjectives reported in semi-open questions. Semi-open questions are useful to capture psychological constructs such as perceptions. However, due to the qualitative nature of adjectives, it is difficult to assign an objective numerical value to them. The proposed model contributes to (1) account for response behavior heterogeneity in the evaluation of a new data type and (2) investigate the use of both discrete and continuous scales. As application example, the estimated ratings of the adjectives are integrated into a hybrid choice model of transportation mode preferences.