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 isn’t 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.