Triangulation is an umbrella term which encompasses a number of ways in which the credibility of qualitative research can improved. For example:
Method triangulation: This means using two or more data gathering techniques within one study (as in case studies which examine one individual, group or organisation) so that the strengths of one method overcome the weaknesses of the others. This can include sign both quantitative and qualitative research methods within the same study, e.g. collecting data using standardised tests to measure specific skills but also conducting semi-structured interviews to find out more about the why (in this person’s opinion) as opposed to the what.
Researcher triangulation: Similar to inter-rater reliability. This is where more than one researcher is used to collect and analyse data. If the data matches then subjectivity is somewhat reduced and credibility arguably improved. However, if both researcher share many traits then they may both have similar interpretations due to their similar starting points. This means it may be useful to use researchers from differing backgrounds, for example. This may be particularly true and interesting in cultural psychology, where research teams may deliberately include indigenous researchers as well researchers from an alternative cultural backgrounds. This links to emic research.
Data triangulation: This term is similar to replication (test-retest) in quantitative research and it essential means that before accepting the conclusions of a research study and using them, (e.g. to design interventions/support programmes etc), qualitative researchers should look for other similar studies and see whether the results are inline. Also, before drawing final conclusions, researchers may collect a second or third set of data from another similar population to check whether what they have found relates to the wider group and sub-groups or just to this one very specific group. This is particularly important in qualitative research due to the very small sample sizes, and niche groups that are investigated.