Research Methods Lesson 2 Validity

Lesson Objective Success Criteria 1.To understand what is meant by the term ‘validity’. To apply your knowledge of internal and external validity to your experiment. Identify a method to assess validity in your experiment. 3. Challenge-: How are different research methods affected by validity, e.g. Does a lab experiment have external validity?

What would happen if? Everyone tasted the cookies together. If other participants saw a participant spit out a bit of their cookie.

Validity The validity of any method of measurement refers to how truly/realistically it measures something. A valid test measures what it is supposed to measure - it does not measure something else! For example, a valid IQ test should really be measuring intelligence and not just measuring general knowledge.

How much the findings of a test/method are due to the manipulation of a variable rather than another factor. It is also called experimental validity. For example, a method/test has good internal validity if the findings do result from the manipulation of the independent variable on the dependent variable. Does it measure what it claims to. Does our cookie experiment have internal reliability? Does our taste survey measure taste? Internal Validity

External validity How much the findings of a test/method can be generalised to different settings. This includes how much the findings can be generalised to other environments (ecological validity) and people (population validity). Does our cookie experiment have external reliability? You may be asked about specific validity issues (including researcher bias, demand characteristics, and social desirability). Look back at your notes on extraneous variables and confounding variables to recap these.

Ways of dealing with issues of validity Ways of dealing with issues of validity: If there is a problem with validity, for example, there is a design fault in an experiment, the psychologist can reword the item on the questionnaire or in the interview to see if there is a better match between the scores on the new test and the already established one.

Methods used to assess validity There are a few techniques that psychologists can use to assess whether their experiment or research has high validity. The techniques are shown in the table below: Face Does the test/method actually look like it is measuring what it is supposed to be measuring? For example, are the questions on a stress questionnaire obviously related to stress? Content Does the test measure the behaviour for which it is intended? You could ask an independent expert to check over your questionnaire to evaluate it as a measurement. Concurrent Does the test/method have a strong positive correlation with an already well-established one that claims to measure the same variable? To do this the participants take both tests to form a correlation. Construct Does the test/method test the theory about the variable that it is supposed to be measuring? To do this, you might look at a definition of stress and consider whether the questions measure stress. Predictive Does the test/method predict a person’s future performance on a test/method? For example, you could take measure blood pressure, people who score highly on the questionnaire should have a higher BP.

Validity of research methods: How are each of the following research methods affected by validity Lab experiments Internal/external ? Field experiments Observations Case studies Quasi experiments