Techniques for testing reliability, on the other hand, can be achieved through the test-retest, alternative-forms, and internal consistency methods. Test-retest method administers an instrument to the same population in two different periods/occasions, and the difference between the scores of the first and second administration determines the reliability of the construct under study. Alternative-forms is similar to test-retest method; only, the flow of the instrument in the second administration is reversed, and the difference of the results of the 1st and 2nd tests determines the instrument's reliability score. Lastly, the internal consistency method looks at the construct's consistency when the instrument is tested itself -- that is, if the instrument will be deconstructed, would it still generate reliability scores at par or higher than the scores generated from other test/techniques? (Smith, 1988:46-47). Under the qualitative research design, reliability and validity...

Ultimately, data validity and reliability in qualitative researches are dependent on the credibility of the individuals and groups who provided the information. And since it would be difficult to determine whether indeed, a source is credible -- in fact, the concept of credibility is difficult to conceptualize and qualify -- triangulation is the best tool to use to test for validity and reliability in qualitative data. In triangulation, analysis of data/information from qualitative methods are triangulated by verifying it against quantitative research findings of similar topic or issue, whether this quantitative study is done in parallel to the qualitative study or not (Golafshani, 2003:603).
References

Golafshani, N. (2003). "Understanding reliability and validity in qualitative research." The Qualitative Report, Vol. 8, No. 4.

Smith, M.J. (1988). Contemporary Communication Research Methods. CA: Wadsworth.