Reliablity and validity

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  • Reliability and validity
    • A method is reliable when different researchers can measure or observe something and get similar results
      • External  reliability
        • this is the ability to produce the same results every time the test is carried out
          • this can be tested using the test-retest method
            • where the test is carried out several times using the same or similar participants
            • may vary due to individual differences, extraneous variables etc
          • Test of correlation between set of two scores
            • high correlation coefficient indicates the test is reliable, low correlation coefficant indicated the test is unreliable
      • Internal validity
        • consistency of a measure within a test
        • ensure that your measure is testing accurately
        • Checked by the split- half method
          • comparing half of the test with the other to check whether the scores of a variable are consistent
    • Improving reliability
      • where possible take more than one measurement from each participant
        • reduces the impact of any anomalous score
      • pilot studies ensure that a measurement works properly and that participants can use any apparatus successfully
      • to ensure that all researchers collect and record data in a standardised way
        • for interviews and observations this may require a period of training
        • directly improve inter-test reliability
      • data should be checked  thoroughly   after being recorded
        • to ensure data isn't written down and entered in the computer wrong
    • Internal validity
      • The ability of the study to test the hypothesis that is was designed to test
        • Is the Dv being affected by confounding variables instead of just the iv
          • the greater control we have over these variables the better the internal validity
      • maybe affected by demand characteristics
        • cues that lead to the tendency for participants to behave in the way they think is required of them
          • eg experimenter bias
      • improving
        • single blind technique
          • participants don't know what condition they are in
          • therefore cant change their responses to please the experimenter
        • double blind technique
          • neither experimenter or participant know which condition they are in
    • assessing validity
      • face validity
        • a judgement of whether the test is valid
          • weakest form of validity testing
      • criterion validity
        • whether the test produces similar results to other tests that measure the same thing
        • objective
        • two types
          • concurrent
            • shows similar findings to another existing measure
          • predictive
            • how well a test predicts future performance
    • external validity
      • how well the results beyond the study can be generalised
      • population validity
        • the degree to which results can be generalised to the rest of the population
      • ecological validity
        • the degree to which findings can be generalised to other situations, places and conditions
        • mundane realism
          • degree to which the setting or procedure reflects real life
        • experimental realism
          • the degree to which the results reflect realistic behaviour
    • internal v external validity
      • the more confounding variables that are controlled the more artificial the study becomes
      • researcher must consider which is more important for his study

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