Imagine that you are conducting an experiment into anti-depressants… https://www.youtube.com/watch?v=z03FQGlGgo0 What is this an example of?

Extraneous and Confounding Variables Demand Characteristics and Investigator Effects.

What is the difference? E.V.s are variables which could potentially interfere with the IV or DV. The researcher should identify these and control them before the study. C.V.s are variables which do interfere with the IV by changing systematically with the IV- which means that in effect you have ended up with an extra IV that you didn’t want!

Types of Investigator Effect Experimenter behaviour effects participant behavior Can you think of any ways that an investigator could do this? Giving the impression that the PP is doing well or poorly Decreasing motivation through negative cues Conveying a dislike for some PPs Expecting a certain result and being biased in what they observe Sharing Expectations with PPs

Demand Characteristics Cues that the participants use to work out the experimental aim They may alter their behaviour as a result either: (1) in line with expectation (pleasing the experimenter) (2) away from expectation (’screw you effect’; Masling, 1966) Booklet Page

Dealing with these issues Standardisation- instructions should be exactly the same for all PPs with the same procedure for each. Randomisation- The materials used e.g. a list of words to recall, should be put into random order, not an order chosen by the experimenter. Single Blind Design- When the PPs are kept naïve to the aims Double Blind Design- When the PPs and the researcher are kept naïve to the aim. Piloting- a small scale practice run through

Two Minute Talk! Prepare a short speech in pairs on; Demand Characteristics Investigator Effects Controlling Investigator Effects Controlling Demand Characteristics You must… Define key terms Give an example Explain the point. Write these up and hand in I will copy and distribute to you all. Prize for the winning pair!

We have covered a lot of new words very quickly- lets take a moments to make sure we know them! You have 5 minutes to review them and to test each other before the key terms Quiz! Key Terms Quiz… Independent Variable Dependent Variable Extraneous Variable Confounding Variable Single Blind Method Double Blind Method Internal Validity Ecological Validity Natural Experiment Quasi Experiment Investigator Effect Demand Characteristics Screw-You Effect Hypothesis Directional Hypothesis Non-directional Hypothesis Operationalisation Lab Experiment Field Experiment