Validity%20and%20Reliability - PowerPoint PPT Presentation

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Validity%20and%20Reliability

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Validity and Reliability General points Candidates should show understanding of validity and reliability. Award up to three marks for a point that is specific and in ... – PowerPoint PPT presentation

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Title: Validity%20and%20Reliability


1
Validity and Reliability
2
General points
  • Candidates should show understanding of validity
    and reliability.
  • Award up to three marks for a point that is
    specific and in detail.
  • If no expression of to what extent award
    maximum 6 marks.

3
What is reliability?
  • Reliability is the consistency of your
    measurement
  • It is the degree to which a method of measuring
    something measures the same way each time it is
    used under the same condition with the same
    subjects.
  • In short, it is the repeatability of your
    measurement.
  • Reliable measures mean the same data would have
    been collected under similar circumstances

4
A Simple example
  • you have a set of broken bathroom scales they
    are four pounds out (the scales will represent
    the methodology you are using to measure
    something)
  • One person weighs you with these scales and
    obtains a result.
  • A second person uses the same scales and weighs
    you
  • The two people, using the same broken scales,
    come to similar measures.
  • The results are reliable. The results are
    obtained by two (or perhaps more) people using
    the faulty scale.
  • Although the results are reliable, they may not
    be valid. That is, by using the faulty scales,
    the results are not a true indicator of the real
    weight.

5
Validity
  • Does the study accurately reflects or assesses
    what the researcher is attempting to measure.
  • While reliability is concerned with the accuracy
    of the actual measuring instrument or procedure,
    validity is concerned with the study's success at
    measuring what the researchers set out to
    measure.
  • Validity depends on the Purpose of the measure
    e.g.. a ruler may be a valid measuring device for
    length, but isnt very valid for measuring volume

6
An example
  • 2007 Question 6

7
Evidence for valid and reliable
  • the survey has been carried out by an independent
    body (MORI)
  • carried out on behalf of a reputable foundation
  • the sample size was fairly large (c 2000)
  • asks a wide range of perception questions that
    gauge public opinion well
  • the survey was carried out over 3 years, so
    trends can be identified
  • fairly recent research.

8
Evidence against valid and reliable
  • representative sample of British residents no
    information about sample other than that
  • percentages some add up to over 100, some to
    less, with no explanation offered to explain
    these anomalies
  • no information on the details of the survey eg
    location, social background of the respondents,
    etc
  • the unclear instruction about how many to choose
    from.
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