Purpose - The conventional methods of evaluating service quality analyze data obtained in ordinal scale that assumes scale continuum. The purpose of this paper is to compare the control boundary model with a proposed method that uses law of categorical judgment, which converts data into interval scale. In this paper, the advantages of using the law of categorical judgment over the control boundary model, a method which uses the data directly, is presented by analyzing customer response data obtained to evaluate quality of service in the Howrah Railway Station, a major railway terminal in eastern India. Design/methodology/approach - Law of categorical judgment has been used for data conversion to interval scale and a comparative analysis is made with the results obtained from control boundary model. Findings - The results obtained from the two techniques show that the proposed method of evaluation is more suitable to the context. Research limitations/implications - The work is limited to the subjective evaluation of the physical and functional services of a railway station. Several other aspects like managerial, behavioral, etc. are not considered. Originality/value - Evaluating service quality in this domain is a difficult task. The paper not only proposes a new method but also compares the results with an existing evaluation model.