Previous studies have found monolinguals and bilinguals use different areas of the brain when solving problems, while bilinguals manifest a cognitive system with the ability to attend to more relevant information while ignoring distractions (Bialystok 2007; Hernandez and Bates 2001). Since the mental process that monolinguals experience when answering survey questions differs from that of bilinguals, they likely encounter different problems in understanding the meaning of questions even in their native language. Therefore, for cognitive interviews aimed at improving the quality of translated questionnaires targeting monolingual non-English speakers, it is crucial to conduct interviews with such respondents to elicit relevant information. However, there has been no standardized tool for identifying these speakers. By using different definitions of monolingual speakers: (1) based on self-rated English reading, (2) based on self-rated speaking, and (3) based on both, we investigate how similar or different these groups are by comparing their demographic characteristics.