This study proposed a new algorithm for calculating the scale values, and then examined the effect of number of options in the Likert scale. In order to assess the effect of number of categories, three subscales of the Big Five Scale were modified into three types of questionnaires, with option numbers as 4, 5 and 7. The category parameters were first estimated by the GPCM model, then using the new algorithm, the scale scores were calculated, finally the converted scale values were obtained. Results show that the 4 and 5 points Likert scales are suitable for the BFS, when the 7-points design is not appropriate for this questionnaire.
Q:
1. how to determined whether the scale values are normally distributed or not? Is it an assumption or definition for the distribution of scale values?
2. probably different numbers of options are preferred by different kinds of questionnaires, if this is the case, when develop or modify items, it should try out various numbers of options?