The credibility standard requires a qualitative study to be believable to critical readers and to be approved by the persons who provided the information gathered during the study. Lincoln and Guba recommend several techniques inquirers may use to enhance the credibility of their research: prolonged engagement, persistent observation, triangulation, peer debriefing, negative case analysis, progressive subjectivity checks, and member checking.

Prolonged engagement means being present in the site where the study is being done long enough to build trust with the participants, experience the breadth of variation and to overcome distortions due to the presence of the researcher in the site. This may mean an entire year or longer for some large studies; or it could mean as little as a month or so for smaller studies. There is no set amount of time a qualitative inquiry should last; but the proper length can be estimated by the inquirer once they have spent some time in the site. If it is apparent that the inquirer was on the site long enough to see the range of things to be expected in such a site, the results produced will be more credible.

Persistent observation is a technique which ensures depth of experience and understanding in addition to the broad scope encouraged through prolonged engagement. To be persistent, the inquirer must explore details of the phenomena under study to a deep enough level that he or she can decide what is important and what is irrelevant and focus on the most relevant aspects.
If it appears that an inquirer learned very little detail about any particular aspects of the phenomenon under study (they just spent a lot of time in one place without ever developing a focus and persistently learning more about it), the results will be less credible to a reader of the final report.

Triangulation means the verification of findings through 1) referring to multiple sources of information (including literature), 2) using multiple methods of data collection, and often 3) acquiring observations from multiple inquirers. In other words, if a conclusion is based on one person’s report, given during one interview to only one interviewer, it is less credible than if several people confirmed the finding at different points in time, during interviews and through unstructured observations, in response to queries from several independent researchers, and in the review of literature. Although all three forms of triangulation are not required for every conclusion, the more the better.

Peer debriefing involves meetings by the inquirer with a disinterested peer (someone who is willing to ask probing questions but who is not a participant in the setting where the study is being conducted) in which the peer can question the methods, emerging conclusions, biases and so on of the inquirer. This technique is meant to keep the researcher honest by having someone else independently point out the implications of what he or she is doing. If a researcher can provide evidence of having done this and show the reader how the report was modified through the influence of the peer, the conclusions will be more believable.

Negative case analysis is an analytical procedure that is meant to refine conclusions until they “account for all known cases without exception.” The process involves developing hypotheses based on extensive fieldwork and then searching for cases or instances within the site under study, which contradict the conclusions represented by the hypotheses. If no contradictory cases are found after extensive searching, the hypotheses are considered more credible because no evidence has been found to negate them. If such evidence is found, the hypotheses are modified to account for the new data associated with the negative cases. This process continues until the hypotheses have been modified to account for all negative cases and no new negative cases can be found. If an inquirer completes such an extensive process, the resulting qualitative inquiry report is considered very credible indeed. It is rare to find extensive use of negative case analysis in single studies; but it is expected in series of inquiries on the same subject by the same inquirers.

Progressive subjectivity checks involve archiving the inquirer’s changing expectations for the study (a priori and emerging constructions or interpretations of what is being learned or what is going on). “If the inquirer ‘finds’ only what he or she expected to find, initially, or seems to become ‘stuck’ or ‘frozen’ on some intermediate construction [interpretation], credibility suffers.” (Guba and Lincoln, 1989, p 238) The inquirer is responsible for revealing his or her biases and preferences in reports, field notes, and the audit trail.

The emic or folk perspectives of the participantsshould be highlighted in the study. It should be clear to the readers that the inquirer discovered something of the viewpoints held by the people he or she studied. If only the inquirer's perspective (often referred to as etic perspective) is present, the study lacks one of the most critical characteristics of a qualitative study, although the inquirer's perspective is also necessary. Likewise issues should emerge during the study and discoveries should be made. If the inquirer's original hypotheses are simply confirmed, qualitative inquiry probably is not the appropriate approach to use.

Member checking is one of the most important techniques for establishing the credibility of a qualitative inquiry. In this process, the data record, interpretations, and reports of the inquirer are reviewed by the members or participants who provided the data– the natives. If they agree that their perspectives have been adequately represented and that the conclusions reached in the report are credible to them, the reader of such a study is likely to be convinced that the qualitative inquiry itself is credible. When the “members” are children, the inquirer may have to find alternative ways to share what they are concluding with them; but often asking people to read segments of a report and then give oral feedback and reaction is sufficient.