Informed consent implies that participants need to have substantial understanding of, and agree voluntarily to, the nature of the research and their role within it. Participants need to have the capacity to consent. Consent is generally recorded, though written agreement may not be necessary or appropriate. In some circumstances, it is justified to deceive participants, or to carry out research without consent (where there is negligible risk and observation occurs in a public space where there is no reasonable expectation of privacy; where there is public interest in allowing the research and there is no other way of conducting it; where a subject is unable to consent) (Hughes et al. 2010). Researchers should, however, avoid assuming a lack of capacity as an excuse for relying on assent – not objecting – or proxy consent from parents, carers, etc. Children and other people with cognitive limitations should, so far as practicable, be asked to give informed consent through materials and processes adapted to their level of understanding. (see also Covert Research).