Declarative data is marketing information obtained directly from an individual through a declarative process, such as an online form, a paper form, or a face-to-face or telephone interview. It allows for the qualification and understanding of that individual for customer knowledge, advertising targeting, or direct marketing purposes. However, its reliability can be affected when the individual feels coerced or pressured into providing this data, particularly in the context of online forms or when the topics discussed are sensitive. It is therefore important to consider these limitations and implement verification measures to ensure the relevance and accuracy of declarative data.