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.
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.
To guarantee that participants understand what they are consenting to, researchers should pay attention to the language they use. They should use the language that their target population will be most comfortable with. As a rule, they should refrain from using technical language and use an 8thgrade level of English. Depending on the methodology you are using, the population and topic you are studying, and the level of risk, informed consent may be implied or explicit, active or passive, and written or oral.
Passive consent. Participants are informed of the study, and are considered to agree to participate unless they specifically decline to be included in the study. This procedure is often used in schools that send forms to parents asking them to allow their students to participate in various studies or activities. Although it yields high participation rates, it should be limited to completely innocuous research (typically not involving minors). It is acceptable for participant observation (ethnographic) projects.