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Validity - PowerPoint PPT Presentation

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Validity. “The extent to which a test or research study measures what it was designed to measure”. Validity. Internal validity The extent to which the research study was properly conducted, so that it produced a truthful result

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“The extent to which a test or research study measures what it was designed to measure”

  • Internal validity
  • The extent to which the research study was properly conducted, so that it produced a truthful result
    • The controls (did anything else affect PPs?)
    • The measurements (accurate & meaningful?)
    • The demand characteristics (could PPs work out the aims & change their behaviour?)

  • External validity
  • The extent to which the study’s results can be generalised beyond the research situation
    • The setting (was it realistic?)
    • The sample (was it representative?)

assessing internal validity
Assessing Internal Validity
  • Did the researcher remove or control all additional factors that could have affected the PPs’ behaviour?
  • Was the behaviour measured an accurate reflection of the relevant psychological processes?
  • Were there any clues (demand characteristics) that could have allowed the PPs to guess the aim?

assessing external validity
Assessing External Validity
  • Was the research conducted in a setting that resembles the relevant real-world setting in all important respects?
  • Did the sample used in the study contain members of all the sub-groups represented in the target population in the appropriate proportions?
    • NB: the target population is not necessarily the general population

validity triangulation
Validity & Triangulation
  • Triangulating means comparing the results of a variety of research studies to see if they all point in the same direction.
  • Where the validity of a study is in doubt, see if the same or similar results were obtained in a study that used a different methodology.

internal validity of milgram
Internal Validity of Milgram

Orne (1966) Says…

Milgram Replies…

The PPs were not really fooled. They were just playing along with the demand characteristics of the situation.

If the PPs weren’t really fooled, why did they get so stressed? This would suggest that they thought the shocks were real.

The stress came from having to play along with the situation. They still didn’t believe they were hurting Mr Wallace really.

If they didn’t believe that Mr Wallace was really getting hurt, why did they ‘cheat’ when the experimenter was absent?

external validity of milgram
External Validity of Milgram



Milgram’s study involved a bizarre task and an artificial situation. People don’t really behave that way in real life.

But Hofling et al found that nurses would obey an order to hurt a patient. This shows that authority can make people do bad things

But the nurses were only doing their job. They thought it was for the patient’s benefit, and most didn’t notice the incorrect dosage

OK, but Bickman (1975) showed that just wearing a uniform increases people’s obedience. That’s what Milgram showed.

external validity of milgram1
External Validity of Milgram



Milgram only used men in his research. That means that we cannot generalise his results to women. We cannot wholly trust his results.

But Milgram did a later study with female pps and found that the rate of obedience was 65% - exactly the same as in male samples.

Milgram only used 40 Fs – a small sample. Kilham & Mann (1974) found only 16% of Fs obeyed – less than the Ms in their study (40%)

That’s a freak finding. The experiment has been done many times, and usually M & F don’t differ, regardless of the culture of the PPs.