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Reliability and validity
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Two key words for evaluating any research: reliability (consistency) and validity (accuracy).
Reliability
Studies with standardised procedures and quantitative data (such as lab experiments and closed questionnaires) are easier to replicate, so their reliability can be checked.
In observations, inter-rater reliability means two or more observers record the same behaviour in the same way.
Qualitative methods (unstructured interviews, case studies) are harder to repeat exactly, so they tend to be less reliable.
Validity
Ecological validity: whether results can be applied to real-life settings. Field and natural experiments usually have higher ecological validity than lab experiments.
Population validity: whether results can be generalised to other people. This depends on the sampling method: a representative (stratified or random) sample gives higher population validity than an opportunity or volunteer sample.
Validity is reduced by extraneous variables, demand characteristics and social desirability (people giving answers that make them look good).
Applying them
Two observers watch the same playground video and record very different numbers of aggressive acts. What does this suggest, and how could it be improved?
- The observers are not consistent with each other: low inter-rater reliability.
- Clear behaviour categories and observer training would help them record behaviour in the same way.
Answer: Low inter-rater reliability; improve with clearly defined behaviour categories and training.
Reliability means consistency: a reliable study gives the same results when repeated, helped by standardisation and quantitative data. Validity means accuracy: ecological validity concerns real life, population validity concerns other people. Lab experiments tend to be reliable but less ecologically valid; qualitative methods can be valid but less reliable.
The interactive lesson includes the diagrams for this topic.
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