Oral consent should be considered when obtaining explicit, active consent is essential, but the risk or discomfort involved in the process is too great to make written consent a valid option. Some populations, such as criminals, undocumented immigrants, or the homeless, may be placed at legal risk, or be suspicious of leaving a written trace, and refuse to participate. Or, the topic of the research may be highly sensitive, because it concerns behavior and attitudes that, even though legal, are socially condemned. Should the records be exposed, or a criminal investigation take place, researchers themselves may become liable. Oral consent is also a valid option for participants that are uncomfortable reading and writing, and may be too embarrassed by the written consent process to participate in research. In that case, the researcher should record the reading of a consent statement, and the clear answers of the participants indicating willingness to participate. The recording verifies informed oral consent.
Written consent. Participants give their consent by filling out a consent form. Written consent guarantees active and explicit consent, thus offering the highest guarantees to the participant. It is most appropriate in studies that contain some level of risk, but also in many studies with no risk above those of daily life, when participants disclose personal or sensitive information, when they are exposed to deception, or any experimental treatment. Experiments and in-depth interviews in particular should consider written consent.
To be informed, consent must be given by persons who are competent to consent, have consented voluntarily, are fully informed about the research, and have comprehended what they have been told. Unless they are emancipated minors, individuals under 18 may never give consent. Also question the legal competence of people affected by mental illness, or institutionalized in the prison system. If a person is not legally competent to give consent, a parent or legal guardian has to give it. The participant may still give assent.
For more details, please take alook at these tattoo consent form sample below!