Agreement to take part in research. This should be based on an understanding of the research project and its aims [see also Informed Consent and Free, Prior and Informed Consent]. In theory consent should be freely given or withheld, as the potential participant prefers. In practice some research, such as national censuses in some countries, is mandatory and those who do not participate may be punished (Kara 2018). The granting of consent is often treated as an event, where in fact it is more of a process that is negotiated and renegotiated as research progresses. Indeed, in some cases renegotiation may be essential, such as in research with people with cognitive impairment or in longitudinal research. (see also Dignity and Respect).