Extension: How could psychologists make sure their IV is the only factor affecting their DV? Discuss with somebody else the answers that you put for your homework on IVs and DVs.

Check your answers against those below – ask if you have any questions. 1) IV = intervention OR usual care DV = number of sexual partners. 2) IV = TV programme in a jumbled order OR TV programme in a logical order. DV = Amount of information recalled from the TV programme. 3) IV = Massage after boxing exercise OR having a rest after boxing exercise DV = Performance on a second set of boxing exercises.

4) IV = Cognitive defusion technique OR urge surfing technique OR relaxation technique. DV = How many chocolates were eaten from a bag given to them by the experimenter. 5) IV = Unattractive (fuller waist, smaller chest) pictures of Caucasian males OR Muscular (V shaped torso, larger chest, narrower waist) Caucasian male. DV = How long nine months old babies gazed at each image.

By the end of this lesson you will be able: * To describe what is meant by the following: Extraneous variables, confounding variables, demand characteristics, investigator effects. * To apply those terms to research examples.

The purpose of conducting a piece of research is to see if your IV affects/changes the DV. For example, if you are investigating the effect of gender on helping behaviour, you want to be sure that any difference in results are due to gender and nothing else..

Sometimes, there are other variables which can affect the DV (how helpful someone is) other than the IV (gender). Consider the following scenario: A woman has fallen over in the street, and you want to see who is more likely to help her – men or women. List as many reasons other than gender that could affect whether someone stopped to help or not.

Factors which can influence the DV other than the IV are called extraneous variables. We do not want these extraneous variables to affect the DV, as we are interested in the effect the IV has on the DV. Therefore, researchers try to control (stop) the extraneous variable as much as they can.

In your booklet, read through the definitions of: Extraneous variables Confounding variables Demand characteristics Investigator effects Extension: Choose a study from your textbook and identify the potential extraneous variables.

* Check your understanding For the following examples (next slide), you need to list as many extraneous variables as you can think of. Put each extraneous variable you list into one of the four categories we looked at. - Confounding variable - Demand characteristic - Investigator effects

* Examples Dabbs et al (2001) investigated whether participants’ levels of testosterone had an effect on how nervous they were in social situations. Kiecolt-Glaser et al (1984) investigated the effect that the stress of exams has on the immune system. Sylva et al (2003) investigated whether some types of pre-school experience were more effective than others at promoting children’s development. Extension: Explain how each study could control for the EV you have identified.

* Consequences: * Validity refers to whether your study measured what it said it measured. * There are two main types: * Internal validity * External validity (more on this later)

* Internal validity For example, imagine I carry out a study looking at the link between exercise and obesity. I give out questionnaires to people asking them about if they own and use a car and how much TV they watch a week. I also ask for their height and weight (to work out their BMI). From looking at the research I conclude that people are obese because they do not exercise. * Concerns with what goes on inside a study. Whether the researcher did test what they intended to test. Discuss: Why can my IV and DV be said to not be measured in a valid way?

* Another example * I want to find out if stress affects mood. So I give participants a maths test and then a questionnaire after the test which assesses their mood. Discuss: Why can my IV and DV be said to not be measured in a valid way? How can extraneous variables affect the internal validity of the study? Extension: Why does it matter if our study lacks internal validity?

* Controlling for extraneous variables: To increase internal validity the researcher needs to control for extraneous variables as much as possible. Discuss: how might they do this? Read through the information on control (random allocation and standardisation) in your booklet. Extension: Choose an experiment from your textbook and write standardised instructions for this experiment.

You are now able: * To describe what is meant by the following: Extraneous variables, participant variables, situational variables, demand characteristics, investigator effects, internal validity. * To apply those terms to research examples.

Due next lesson: 1) Complete the activity on extraneous variables. Preparation for next lesson: Think about the downsides of having control over all extraneous variables.