In my own training as a therapist triangulation meant the detouring of conflicts or fears between two members of a family through another, often the detouring of marital conflict through a child......in Qualitative research however it is a central concept and tool when it comes to establishing a rigorous study, one that has a degree of trustworthiness beyond that which is possible through a simple straightforward thematic analysis on grounded theory design
Triangulation essentially means using more than one research strategy to come to your findings..there are many types
1. Methodological triangulation
This can involve mixing quant and qual methods or mixing qual methods. If, for example, you conducted a qual interviews with participants of a RCT, exploring "striking moments" or times when clients felt breakthroughs had been made you would have a much more robust trial and a more robust qual study.....each would compliment the other, with both objective and subjective explorations of what works.....
2. Theoretical Triangulation
I know in grounded theory we are told to try and be a theoretical tabula rasa but one can equally deal with the problem of bias by leaning into it rather than away from it. Purposefully analyzing data from multiple theoretical positions and coming up with an integration can also be a powerful tool for ensuring you arent just using one lens.
3. Investigator Triangulation
Using multiple researchers during the coding process, including cross-coding, collaborative coding across disciplines, and researcher-participant corroboration
Heres a great little paper Triangulation: Establishing the Validity of Qualitative
Studies Lisa A. Guion, David C. Diehl, and Debra McDonald
Validity, in qualitative research, refers to whether the findings of a study are true and certain—“true” in the sense that research findings accurately reflect the situation, and “certain” in the sense that research findings are supported by the evidence. Triangulation is a method used by qualitative researchers to check and establish validity in their studies by analyzing a research question from multiple perspectives. Patton (2002) cautions that it is a common misconception that the goal of triangulation is to arrive at consistency across data sources or approaches; in fact, such inconsistencies may be likely given the relative strengths of different approaches. In Patton’s view, these inconsistencies should not be seen as weakening the evidence, but should be viewed as an opportunity to uncover deeper meaning in the data.
Here's another Why Triangulate?
This article discusses triangulation as a strategy for increasing
the validity of evaluation and research findings. Typically,
through triangulating we expect various data sourcesand methods
to lead to a singular proposition about the phenomenon being
studied. That this is not the case is obvious to most researchers
and evaluators. Given that this expectation is unrealistic, an alter-
native perspective of triangulation is presented. This alternative
perspective takes into account that triangulation results in con-
vergent, inconsistent, and contradictory evidence that must be
rendered sensible by the researcher or evaluator.