Validity is an issue that has been described in great deal by advocates of quantitative researchers. Validity in qualitative research is defined as the extent to which the data is plausible,credible and trustworthy; and thus can be defended when challenged. There have different opinions on validity with some suggesting that the concepts of validity is incompatible with qualitative research and should be abondoned while others argue efforts should be made to ensure validity so as to lend credibility to the results.
Types of Validity
Maxwell, 1992, in Understanding and validity in qualitative research, Harvard Educational Review identifed THREE types of validity in qualitative research:
Strategies to Promote Validity of Qualitative Research
1) Extended fieldwork or Prolonged Engagement On-Site
If possible qualitative researchers should collect data over an extended period of time. The length of time will depend whether you are able to get an
accurate picture of the phenomenon examined. For example, your
observations of classroom interactions would different one weeks prior to
preparation for sports day compared to a normal school week. So that week
prior to sports day would not be a typical week for a school.
2) Low inference descriptors
Use description phrased very close to the participants' accounts and
researchers' field notes. eg. verbatims (i.e. direct quotes) are a commonly
used type of low inference descriptors.
3) Triangulation
Cross-checking information and conclusions
Data triangulation: use multiple data sources to help understand a phenomenon
Method triangulation: use of multiple research methods to study a phenomenon
Investigator triangulation: use multiple investigators (or researchers) when collecting and interpreting the data
Theory triangulation: use of multiple theories and pespectives to help interpret and explain the data
4) Participant feedback or Member Checking
Discuss with the partcipants your interpretations and conclusions for
verification and insight. Go bakc to those people and check the observations
you made of them, i.e. is this what you meant? is this what you did?
5) Peer review or Peer Debriefing
Discuss your interpretations and conclusions with other people which:
include a peer who is not interested but who could be critical and challenge your data
include a peer who is interested in your study and can provide insights about your data
5) Negative case sampling
Examine cases that are contrary to your expectation which help you confirm
or disconfirm interpretations of the cases you are studying
6) Reflexivity or Neutrality
You critically examine yourself to detect potential biases and inclinations
that may affect your conclusions. Even though no data collected is 100%
objective, the researcher should convince readers that a high level of
objectivity has been maintained. If you used another observer, was there
consistency or high inter-rater reliability (used in quantitative research)
between the observers?
7) Pattern matching
Try to predict results that form a pattern and than compare the extent to
which the actual results agree with the predicted pattern
8) Audit Trail
The researcher should have good documentation so that another researcher
can easily replicate the research. More importantly, it allows someone to
challenge or confirm the interpretation of the data made by the researcher.
How do qualitative researchers reckon with the Validity Issue?
Below is a summary by R. Burke Johnson (1997) in the article Examining the Validity Structure of Qualitative Research, Education, 118(2): p. 282-290 and Carolyn Benz & Isadore Newman (1998), Qualitative-Quantitative Research Methodoloy: Exploring the Interactive Continuum, Carbondale: Southern Illinois University Press; on addressing the validity issue:
It is so much easier with quantiative research methods !!!!!
The GENERALISABILITY Issue of Qualitative Research
External validity (the extent to which the results of the study can be generalised to another setting or group of people) is an important issue in quantitative research. How about qualitative research? Isadore and Newman (1998), state that,
That one should be able to generalize underlies science. However, we are
unwilling to accept fully that generalizability is consistent with the qualitative
paradigm...... in principle, generalizability is the purpose of quantitative, not
qualitative research. In fact, we have assumed that, if the purpose of
the research is to generalize, one should employ quantitative methodology
(p.54).
However, there are qualitative researchers who argue that some attempt should be made to generalise the findings. The in-depth description of phenomenon is sufficiently comprehensive to allow the qualitative researcher to generalise to each and every member of the population. Benz and Newman (1998) argued that the desire to allow for some form of generalisation to a wider audience has put pressure on qualitative researchers to create ways in which generalisation can be enhanced. They proposed the following concepts:
a) Applicability: Can this research be applied to other samples?
It should be remembered that there is no test of signficance and one cannot make "sample-to-population" statements. The deep description of the characteristics of the subject/sample being studied may allow one to conclude the extent to which it is comparable to other subjects/samples. If the subjects/sample are comparable, then one would be more comfortable to make generalisations.
b) Context Limited: Do the findings of the research hold up in other settings or situations?
If it can argued that what is being observed is not dependent on the context, (i.e. it is not "context limited") and may be transferred to other contexts; then the findings may be generalised.
c) Replicability: What is the likelihood that a given outcome or event will happen again if given the same circumstances?
To replicate the study is the most difficult to accomplish because we are dealing with the natural setting which will invariably change. Unless there is data to show these changes, it will advisable to be cautious when claiming that the study can be replicated.
1) Descriptive Validity
The accuracy of what is reported by the researcher (the events, the objects, the behaviours, the setting, etc). For example, what that is reported actually happened; what that was heard or observed is accurately reported.
2) Interpretive Validity
Accuracy in interpreting what is going in the minds of the participant and the degree to which the participant's views, thoughts, feelings, intentions and experiences are accurately understood by the reseacher.
3) Theoretical Validity
The extent to which the theoretical explanation developed fits the data and therefore is credible and defensible.
Validity is an issue that has been described in great deal by advocates of quantitative researchers. Validity in qualitative research is defined as the extent to which the data is plausible, credible and trustworthy; and thus can be defended when challenged. There have different opinions on validity with some suggesting that the concepts of validity is incompatible with qualitative research and should be abondoned while others argue efforts should be made to ensure validity so as to lend credibility to the results. 
