In one line: Validity is the extent to which a measure, or a study, represents what it claims to represent.
A company sells a "creativity test". Candidates have three minutes to write down uses for a brick, and the score is the number of uses listed.
The test is consistent: people who write fast score high every time. Whether it measures creativity is another matter. Validity is the question of what a score means, and it cannot be settled by showing that the score is steady.
Remember: Reliability is about the numbers. Validity is about what the numbers stand for.
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Key idea: A measure stands in for a construct. Three questions test how well it does so.
Three checks on a measure
Construct validity
Does the measure reflect the construct, and only the construct?
A count of uses for a brick reflects speed of writing and fluency with words as well as creativity.
Face validity
Does it appear, to a reasonable observer, to measure the construct?
It is the weakest check, because appearances can mislead, but a measure without it is hard to defend.
Content validity
Does it sample the whole of the construct?
Creativity includes originality and usefulness. A test that counts ideas without judging them covers one part.
Construct · Face · Content
Construct validity is supported when a measure agrees with other measures of the same construct and with real outcomes. If scores on the brick test had no relation to creative work judged by experts, its construct validity would be in doubt.
Exam tip: A criticism of construct validity names a rival construct.
"The test may measure writing speed" is a criticism. "The test may not be valid" is not.
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Key idea: Validity also applies to a whole study: to the cause it claims, and to the people and settings it claims to speak for.
Internal validity
- The change in the DV is due to the IV alone
- Threatened by confounding variables, expectations, order effects
- Raised by random allocation, control and blinding
External validity
- The finding holds beyond the study
- For other populations, settings (ecological) and times
- Raised by representative samples and lifelike tasks
The two often pull in opposite directions. Memory research shows it well. Lists of unrelated words, learned in a silent room, allow exact control and clear conclusions about cause. They also resemble almost nothing that people remember in daily life.
Applying a finding to a wider population is called generalising. It is justified when the sample represents that population.
The trade-off: Neither kind is simply better.
A body of research is strongest when controlled studies and lifelike studies point the same way.
Key idea: Qualitative research asks the same two questions under different names: is the account true to the participants, and where else might it apply?
Credibility
- The counterpart of internal validity
- Do the findings give a true picture of what participants think?
- Threatened by researcher bias and by participants who are not frank
Transferability
- The counterpart of generalising
- Could the findings apply to another group or setting?
- Judged by the reader, case by case
Ways to improve credibility
Reflexivity
The researcher examines and reports how her own position may have shaped the questions and the analysis.
A decision trail
Every decision in collecting and analysing the data is recorded, for example in a journal, so that others can follow and question it.
Credibility checks
Participants read the transcripts or the findings and say whether they are accurate. This is also called member checking.
Triangulation
A second researcher analyses the data independently (researcher triangulation), or a second method is used on the same question (method triangulation).
Reflexivity · Trail · Checks · Triangulation
What transferability needs: The reader can judge transfer only if the report describes the participants and the setting in detail.
Findings transfer where the new setting resembles the original one, and where other studies have found the same.
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How this is asked: On Paper 3, one 6-mark question is about a qualitative study in a source. Two of its three possible wordings belong here: how the researcher could improve the credibility of the findings, and how far the findings are transferable.
On Paper 2, validity is part of the concept of measurement.
The pattern for credibility, 6 marks
- Say what credibility means, in one sentence.
- Find what in the source threatens it: the researcher's position, a lone analysis, participants who may hold back.
- Give a strategy for each threat, and say why it would help.
- Credit anything the researcher already did.
- Note a limit of a strategy.
The trap: terms from experiments: Random allocation and control groups do not belong in an answer on a qualitative study.
Use the strategies that fit: reflexivity, checks with participants, triangulation.
Discuss how the researcher could improve the credibility of the findings in the source below.
Source: A researcher wanted to understand why students drop out of a university's first-year engineering course. She carried out semi-structured interviews with eleven students who had left the course in the past year. She had taught some of them herself. The interviews were recorded and transcribed. She analysed the transcripts alone and reported two themes: "poor preparation at school" and "lack of effort". No former student saw the report before it was presented to the department.
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