Ordinal Data Models for No-Opinion Responses in Attitude Survey Maria Iannario 1 , Marica Manisera 2 , Domenico Piccolo 1 and Paola Zuccolotto 2 Abstract In analyzing data from attitude surveys, it is common to consider the “don’t know” responses as missing values. In this article, we present a statistical model commonly used for the analysis of responses/evaluations expressed on Likert scales and extended to take into account the presence of don’t know responses. The main objective is to offer an alternative to the usual custom to treat them as missing values by considering them as a source of uncertainty. The original proposal in this article is the introduction of the relevant covariates in order to discriminate subpopulations that can show different behaviors in choosing between a substantive response and the don’t know option. Keywords category rating, don’t know responses, ordinal data, CUB models, covariates Introduction This article is concerned with the analysis of ordinal variables collected in surveys, which allow to consider the don’t know option of respondents. We 1 University of Naples Federico II, Naples, Italy 2 University of Brescia, Brescia, Italy Corresponding Author: Marica Manisera, University of Brescia, Contrada Santa Chiara, 50, Brescia 25122, Italy. Email: marica.manisera@unibs.it Sociological Methods & Research 1-27 ª The Author(s) 2018 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/0049124118769081 journals.sagepub.com/home/smr