Triangulation: A Core Concept in Qualitative Research

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

Abstract


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?
SANDRA MATHISON

Abstract


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.