Validity

• Types of validity

  Validity can be separated into internal and external validity.
• Internal validity

  refers to things that happen “inside” the study

  • Internal validity is about control and realism.
  • It is concerned with whether we can be certain that it was the IV which caused the change in the DV. If aspects of the experimental situation lack validity, the results of the study are meaningless and we can make no meaningful conclusions from them.
  • Internal validity can be affected by a lack of mundane realism. This could lead the participants to act in a way which is unnatural, thus making the results less valid.
  • Internal validity can also be affected by extraneous variables.
• External validity


  The extent to which the results of a study can be generalized to other situations, people, stimuli, and times
• External validity is affected by internal validity

  You cannot generalise the results of a study that was low in internal validity because the results have no real meaning for the behaviour in question
• Aspects of external validity


  • The place where the research was conducted (ecological validity)
  • The people who are being studied (population validity)
  • The historical period (temporal validity)
• Ecological validity


  The extent to which research findings can be generalized from the research setting to everyday life
• Population validity


  The extent to which research findings can be generalized from the sample studied to the broader population
• Temporal validity


  The extent to which research findings can be generalized from one historical period to another
• If a study involved just students or only males etc., then it may not be appropriate to generalise the findings to all people
• If a study was conducted in the 1950s, it may not be appropriate to generalise findings to people today because many other factors affect behaviour now
• This is not true of all 'old' studies e.g. the 1950's brain is not different from today's brain
• Assessing validity

  Number of ways to assess validity
• Content validity


  Does the method used actually seem to measure what you intended? For example,

  does an IQ test actually measure levels of

  intelligence, or is it measuring ability to solve

  puzzles which is a different construct.

  To ensure content validity, a panel of experts

  (on IQ for example) may be asked to assess

  the measure for validity
• Concurrent validity


  How well does the measure agree with existing measures? For example, does our IQ test agree with established tests of IQ? We can ensure concurrent validity by testing participants with both the new test and the established test. If our test has concurrent validity, there should be high agreement between the scores on both measures.
• Construct validity


  Is the method actually measuring all parts of what we are aiming to test? For example, if we use a maths test to test intelligence, we are missing out on other factors involved such as linguistic ability or spatial awareness. To maintain construct validity, we need to define what it is we are aiming to measure, and ensure that all parts of that definition are being measured.
• Predictive validity


  Is our measure associated with future behaviour? For example, if someone scores high on our IQ test, we would expect them to perform well in GCSE exams, or do well in their career. This is similar to concurrent validity. We can investigate predictive validity by following up our participants to see if future performance is similar to performance on our measure.
• Face validity


  A means of establishing validity by considering the extent to which a test or questionnaire looks as if it is measuring what it intends to measure. If we are measuring IQ we should not include any questions about a person’s favourite ice cream. A person themselves can sometimes assess whether a measure taken from them is valid.