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.
Active consent. Participants indicate their willingness to participate by agreeing to a specific statement, and then are included in the study. This is the most common, and recommended, form of consent for research.
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.
Implied consent. Participation in the study is proof of consent. This is acceptable for studies that provide anonymity, such as opinion surveys. A statement at the top of the instrument should clearly state that by filling it, the participant consents to participate, but does not wave any of their rights as research participant. Projects using implied consent should use the consent statementtemplate provided in this website, or a similar document, in their proposal. It provides active implied consent.