1. Imagine that you are conducting an experiment into anti-depressants…
What is this an example of?

2. Extraneous and Confounding Variables
Demand Characteristics and Investigator Effects.

3. 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!

4. 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

5. 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

6. 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

7. 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!

8. 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