2. Reliability and validity
• The terms reliability and validity are most
commonly used in quantitative research
• In quantitative research you would use
research methods that are measurable,
numerical and statistical
• They are usually cause and effect based and
therefore reliability can be tested and re-
tested
3. Reliability and validity
• In qualitative research, the purpose is not to
prove something to be reliable and valid in a
measured way but rather to provide more in-
depth understanding of a phenomenon.
• In qualitative studies, it is argued that using
reliability and validity as the way to ensure
feasibility does not provide the type of
trustworthiness needed
4. Reliability
• Reliability is about the credibility of your
research and it demands consistency.
• If someone examines your research will it
stand up to this scrutiny?
• In other words will someone to be able to re-
test your data and obtain the same results
5. Reliability
• Reliability is about the credibility of your
research and it demands consistency.
• If someone examines your research will it
stand up to this scrutiny?
• In other words will someone to be able to re-
test your data and obtain the same results
6. Reliability
• “Reliability refers to the fact that different
research participants being tested by the
same instrument at different times should
respond identically to the instrument.”
(Mouton 2007:144).
7. Reliability
• Another term used when looking at reliability is
generalisation.
• Reliability can be seen as the extent to which the
results can be generalised and similar results
obtained if the research was tried again.
• This term generalised is important in quantitative
studies when looking at reliability because
reliability in quantitative research is very much
about if your results can be generalised to
different measuring occasions (Collis & Hussey
2003: 145; Welman & Kruger 2003:139).
8. Type of Reliability What is it How to Establish it
Inter-rater or inter-coder This is a measure of agreement Different participants used but with the same
method/tool/instrument administered
Test-re-test This is a measure of stability The same participants used but the
method/tool/instrument is administered at different
times
Parallel forms This is a measure of equivalence Different participants are used at the same time and
using a different method/tool/instrument
Split-halves This also measures equivalence Since it is often difficult to (like with the parallel form)
have a different method/tool/instrument. The split
halves instead would take the method/tool/instrument
and split it into two equivalent halves and correlate those
scores together.
Internal Consistency This is about how consistently each item measures the
same thing (construct)
Correlate the performance on each item with the
performance across participants
9. Validity
• Validity is about finding out if the research
method/tool/instrument that you selected
obtained the information that it was supposed to.
• In other words, the extent to which the
tool/method/instrument that was selected
actually reflects the reality of those constructs
that were being measured.
• The question to ask for seeing if you have validity
is do the findings actually reflect what is
happening in the given situation? (Babbie &
Mouton 2001:122; Collis & Hussey 2003:58-60;
10. Validity
• Validity is about finding out if the research
method/tool/instrument that you selected
obtained the information that it was supposed to.
• In other words, the extent to which the
tool/method/instrument that was selected
actually reflects the reality of those constructs
that were being measured.
• The question to ask for seeing if you have validity
is do the findings actually reflect what is
happening in the given situation? (Babbie &
Mouton 2001:122; Collis & Hussey 2003:58-60;
11. Type of Validity Questions you would ask related to this type of validity
Content validity Is the test representative? Does the measurement represent the specific content?
Sampling validity This is similar to content validity.
Face validity Does the test look like what it is supposed to? Is it well designed?
Construct validity Does the test correspond to other variables? Does it measure what it is meant to? “Is
there agreement between a theoretical concept and a specific measuring device or
procedure? For example, a researcher inventing a new IQ test might spend a great deal of
time attempting to "define" intelligence in order to reach an acceptable level of construct
validity.” (Colorado State University 2013)
Criterion-related validity/instrumental validity Does the test accurately predict future behaviour? How accurate is the measure
or procedure when compared to another?
12. Internal Validity
• Internal validity asks if the method and design will
answer the research question that you want it to.
• In other words there must be no errors in your
design of your research and your method must
match the question.
• Internal validity is mainly used in quantitative
research.
• Internal validity also relates to possible errors in the
results even though controls were in place to prevent
it
13. External Validity
• External validity is also mainly used in quantitative
research
• It is focused on the ability to generalise findings from
a specific sample to a larger population.
• External validity refers to how whatever results we
get from our chosen sample that we need to be able
with confidence say we could get similar results from
the rest of the population, if we applied our same
method and design to our question.
14. External Validity
• In other words you would ask yourself will I be
able to generalise my results outside of my
sample to the general population?
• Neuman (1997:145) gives an example of
external validity by explaining that if
something happens in a controlled
environment such as a laboratory would the
findings be able to be generalised when they
are tested outside of that controlled
environment.
15. Trustworthiness
• Reliability and validity cannot be measured in the same
in qualitative research because the answers are not
objectively measurable they are unique to each
individual’s experience.
• Some qualitative researchers do still use the terms
reliability and validity but the way in which they show
reliability and validity differs.
• In qualitative research researchers look for
trustworthiness, which will represent the same thing
for a research project as reliability and validity but it is
more suitable for qualitative research methods and
studies.
16. Four areas of trustworthiness
• Lincoln and Guba (1985) state that within
qualitative research, there are four criteria
that must be used in order to make sure that a
qualitative study would be considered to be
feasible.
• These are the four areas of trustworthiness
17. Four areas of trustworthiness
• Credibility – This is similar to internal validity in
quantitative studies.
• Transferability - This is similar to external validity
or generalisability in quantitative studies.
• Dependability - This is similar to reliability in
quantitative studies.
• Confirmability - This is in preference to what
quantitative studies call objectivity.
(Collis & Hussey 2003:278-279; Lincoln & Guba
1985; Shenton 2004)
18. Credibility
• Credibility is about how accurate your
interpretation of the data is compared to the
original data that your participant gave you in
your research.
• Credibility is increased when the researcher
spends long periods with the participant and
also by using mixed methods (more than one
method) of data collection
19. Transferability
• Transferability is based on the ability of the
findings to be applied to a similar situation
and then obtain similar results.
• This would allow for generalisation within an
approach that does not lend itself to
generalised findings.
• In other words, it is the degree to which the
results and analysis can be applied beyond a
specific research project
20. Dependability
• Dependability is about the quality of the
process of integration that happens between
the data collection method, data analysis and
theory generation
21. Confirmability
• Confirmability is about how well the data
collected supports the findings and
interpretation of the study.
• It examines how well the findings flow from
the data and it requires the researcher to have
described the research process fully
