 For experimental philosophers seeking to investigate the sources, character, and distribution of intuitions of philosophical interest, the primary method has consisted of asking subjects questions about hypothetical scenarios, or less frequently, about principles or generalizations. The evidence has been responses (whether binary [yes/no] responses or graded [Likert scale] responses) to such survey questions. Those pursuing the sources project and the variation project also aim to determine which factors co-vary with answers—cultural or ethnic group, socio-economic status, region of brain or cognitive processes implicated in answering the question, psychopathology, order of questions, framing of questions, etc.