Data Triangulation In Case Study Research Method

This article is about verification of research data. For other uses, see Triangulation (disambiguation).

In the social sciences, triangulation is often used to indicate that two (or more) methods are used in a study in order to check the results of one and the same subject. "The concept of triangulation is borrowed from navigational and land surveying techniques that determine a single point in space with the convergence of measurements taken from two other distinct points."[1] The idea is that one can be more confident with a result if different methods lead to the same result.

Triangulation is a powerful technique that facilitates validation of data through cross verification from two or more sources. In particular, it refers to the application and combination of several research methods in the study of the same phenomenon.[2]

  • It can be used in both quantitative (validation) and qualitative (inquiry) studies.
  • It is a method-appropriate strategy of founding the credibility of qualitative analyses.
  • It becomes an alternative to traditional criteria like reliability and validity.
  • It is the preferred line in the social sciences.

By combining multiple observers, theories, methods, and empirical materials, researchers hope to overcome the weakness or intrinsic biases and the problems that come from single method, single-observer and single-theory studies.


The purpose of triangulation in qualitative research is to increase the credibility and validity of the results. Several scholars have aimed to define triangulation throughout the years.

  • Cohen and Manion (2000) define triangulation as an "attempt to map out, or explain more fully, the richness and complexity of human behavior by studying it from more than one standpoint."[3]
  • Altrichter et al. (2008) contend that triangulation "gives a more detailed and balanced picture of the situation." [4]
  • According to O’Donoghue and Punch (2003), triangulation is a “method of cross-checking data from multiple sources to search for regularities in the research data."[5]


Denzin (1978) identified four basic types of triangulation:[6]

  • Data triangulation: involves time, space, and persons
  • Investigator triangulation: involves multiple researchers in an investigation
  • Theory triangulation: involves using more than one theoretical scheme in the interpretation of the phenomenon
  • Methodological triangulation: involves using more than one method to gather data, such as interviews, observations, questionnaires, and documents.


  1. ^Rothbauer, Paulette (2008) "Triangulation." In Given, Lisa (Ed.), "The SAGE Encyclopedia of Qualitative Research Methods." Sage Publications. pp. 892-894.
  2. ^Bogdan, R. C. & Biklen, S. K. (2006). Qualitative research in education: An introduction to theory and methods. Allyn & Bacon. ISBN 978-0-205-51225-6.
  3. ^Cohen, L., & Manion, L. (2000). Research methods in education. Routledge. p. 254. (5th edition).
  4. ^Altrichter, H., Feldman, A., Posch, P. & Somekh, B. (2008). Teachers investigate their work; An introduction to action research across the professions. Routledge. p. 147. (2nd edition).
  5. ^O'Donoghue, T., Punch K. (2003). Qualitative Educational Research in Action: Doing and Reflecting. Routledge. p.78.
  6. ^Denzin, N. (2006). Sociological Methods: A Sourcebook. Aldine Transaction. ISBN 978-0-202-30840-1. (5th edition).

The one primary advantage to using the case study method in your dissertation is that it usually allows you to concentrate on an issue, problem, or concern that is directly or indirectly related to your job or career. For every dissertation student I have worked with, who decided to use the case study method, their Purpose of the Study had something to do with their profession. They had been immersed in or had observed a situation that meant something to them. They cared a great deal about the people involved in the case.

For dissertations, when you start your case study research you may want to follow the recommendations of Robert K. Yin, who I believe is the best methodologist available. His book, Case Study Research: Design and Methods is regarded by numerous universities as the best primary source for the case study method. It is now considered the “bible” for case study methods. It is well organized and his writing style is easy to follow. This is rare bonus in academic writing.

Sources of Evidence

You will notice that he suggests six sources of evidence: documentation, archival records, interviews, direct observations, participant-observation, and physical artifacts. Most universities will accept at least three of these in a case study design. More sources of evidence are better, but only if these can be properly recorded and validated. If it is possible to conduct interviews with individuals, who are knowledgeable about the topic of the study, I suggest you do so. Interviews make it easier to humanize your study. You will no doubt gain more insights and better perspectives that would not be so apparent through other evidential sources.

Yin (2009) states, “For case studies, the most important use of documents is to corroborate and augment evidence from other sources.” (p.103) He also states, “Because of their overall value, documents play an explicit role in any data collection in doing case studies.” (p.103) This is a fundamental point for you as a dissertation writer to pay attention to – the credibility of your case study is directly related to the quality of the data you acquire from various sources of evidence.

Creating a Database

I suggest that you create a table or some sort of data file about the documentation and/or archival records you have gathered or plan to use. You might want to consider these categories:

  1. Code number
  2. Name (if it does not have a title, give it a generic name of your own)
  3. Source
  4. Date published or date obtained
  5. Type of data included, and
  6. One or more descriptive statements about the data.

Yin (2009) on pages 118 and 119 refers to what he calls Create a Case Study Database. By validating the importance of a case study database he states, “… without a case study database, the raw data may not be available for independent inspection.” (p. 119) He goes on to write, “…every case study project should strive to develop a formal presentable database, so that in principle, other investigators can review the evidence directly and not be limited to the written case reports. In this manner a case study database markedly increases the reliability of the entire case study.” (p. 119) I would add that without a database, it will be very difficult to present accurate findings and you could become overwhelmed with the data sources.

Why Use Multiple Sources of Evidence

By placing greater emphasis on your documents and archival records, you may better confirm the findings from the interview transcripts. This is a form of triangulation.  In other words the documents help you to validate the findings from the interviews. Yin (2009) states: “Without multiple sources, an invaluable advantage of the case study strategy will have been lost. Worse, what started out as a case study may turn into something else.” He calls this something else an “interview” study. This is not what you want. He is not discounting the value of interviews. He is just claiming that without documents or archival records, it would be hard to adequately conduct a case study.

Triangulation of Interview Data

In qualitative methodologies, such as case study, grounded theory, and phenomenology, you can improve the validity of your findings if you use one of various forms of triangulation.

Here is an excellent and comprehensive definition of “triangulation” from Thomas A. Schwandt in his book, The Sage Dictionary of Qualitative Inquiry, 3rd edition, Sage Publications, (2007):

“Triangulation is a means of checking the integrity of the inferences one draws. It can involve the use of multiple data sources, multiple investigators, multiple theoretical perspectives, and/or multiple methods.” (p. 298) He continues: “The strategy of triangulation is often wedded to the assumption that data from different sources or methods must necessarily converge or be aggregated to reveal the truth.” (p. 298) This is the most comprehensive definition I have found for triangulation. It easily supports the following three-step approach I have suggested to many clients, who conducted interviews in their phenomenological or case study designs:

Step One – Interviews are conducted and audio-taped. Note-taking is not a good substitute for taping since it distracts the interviewer from what the participant is saying and contributes to missed opportunities for more probing questions for clarification. Two common issues that may need more description are the participants’ use of empty or fluff words like “tough.” What does tough mean? You will want to ask for more information and/or description. When they say “tough,” exactly what do they mean? A second issue comes up from time to time. A participant may be overly vague, such as “That was no fun.” This statement has no real meaning to you as a researcher. You will want to interrupt them and ask for the statement or comment in question to be described in some way. You could ask, “When you say ‘That was no fun,’ what do you mean? Can you tell me more about that?”

Step Two – Audio-tapes are transcribed and returned to participants for their review and approval. This is what W. Paul Vogt in the Dictionary of Statistics and Methodology: A Nontechnical Guide for the Social Sciences (2005) calls “member check (or validation).”  His definition is “The practice of researchers submitting their data or findings to their informants (members) in order to make sure they correctly represented what their informants told them. This is perhaps most often done with data, such as interview summaries; it is less often done with interpretations built on those data.” (p. 190-191)

Step Three – Researcher collaborates with an “outside evaluator” or “external auditor” during data analysis (identifying meaning units from the transcripts and making the conversion into themes). Schwandt states, “This is a procedure (of auditing) whereby an independent, third-party examiner systematically reviews an audit trail maintained by the inquirer.”  “An audit trail is a systematically maintained documentation system.” (p.12)

You will find that, with the inclusion of this form of triangulation in your data analysis procedures, your chair will appreciate your efforts to use a validation strategy and the university will be more willing to approve your methodology. Every doctoral student I have worked with, who has used my three-step approach to triangulation, has had their IRB application approved. It has two major advantages: (1) it is easy to conduct and (2) the audit trail is traceable. This process lessens the concerns many chairpersons have over possible subjectivity of the findings.

Convergence and Chain of Evidence

You may want to consult Yin’s (2009) Figure 4.2, Convergence and Nonconvergence of Multiple Sources of Evidence, on page 117 and Figure 4.3, Maintaining a Chain of Evidence, on page 123. Both of these should give you a visual snapshot and better understanding of the value of creating a case study database and using triangulation.

I would also encourage you to mention both Yin (2009) and Gerring (2007) or another researcher at the beginning of Chapter Three, Methodology, and state that you are “adapting” their guidelines for data collection, data analysis, and presentation. By adapting your approach from theirs, you reduce the requirement to follow precisely what each one recommends. Many students find it extremely difficult to follow all aspects of one approach. By incorporating various aspects from two or more sources, you will have more flexibility with your procedures. Some committee chairs may also view you as more creative since you are integrating your methodology from more than one source.

Data Analysis

The process of analyzing transcripts and other sources of evidence for natural meaning units is an ongoing process. As you become more familiar with the data, you have new insights and a better understanding of what the participants are saying. So if you see a few natural meaning units without assigned idiographic themes, you can re-consider these and add appropriate themes. You also have the option of re-naming previously identified idiographic themes.

In case study data analysis, I believe it is best to first respond to each interview question and later try to summarize the findings relevant to the research question or questions.



Ellet, William. (2007). The Case Study Handbook: How to Read, Discuss, and Write Persuasively About Cases. Boston, MA: Harvard Business School Press.

Gerring, John. (2007). Case Study Research: Principles and Practices. New York: Cambridge University Press.

Yin, Robert K. (2009). Case Study Research: Design and Methods, 4th ed. Thousand Oaks, CA: Sage Publications

Case Study Dissertations (Here are three that can serve as excellent models.)

Culbertson, Danielle M. (2012). Effective Mathematics Instructional Strategies for Middle School Students. Walden University, Minneapolis, Minnesota.

Ruvarac, Angelica. (2010). Crisis Communication: Perspectives of  Stakeholders in the Housing Crisis. Purdue University, West Lafayette, Indiana.

Saul, Robert. (2012). A Case Study of Online Degree Course Design and Performance of Online Learners. Northcentral University, Prescott Valley, Arizona.

Recommended citation for this report:

Wargo, W.G. (2014). A.I.C. Report #20, Case Study Method in Qualitative Research. Menifee, CA: Academic Information Center.

If you have questions about any aspect or point in this report, please contact me at or call (951) 301-5557.


Tags:Angelica Ruvarac, Case Study method, creating a database, Danielle M. Culbertson, John Gerring, Robert Saul, Robert Yin, sources of evidence, triangulation of interview data, William Ellet




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