Distinguishing between Extraneous and Confounding Variables

1. Distinguishing between Extraneous and Confounding Variables Extraneous Variable: Any variable that has the POTENTIAL to influence the DV in an experiment and bias the results. Confounding Variable: A variable that DOES have an unwanted effect on the DV in an experiment. Results become bias as it cannot be determined whether results are caused by IV or confounding variable.

2. Independent Groups design POPULATION SELECTION SAMPLE ALLOCATION Experimental Group - IV present Control Group – IV absent Measure effect on DV Measure effect on DV Is there a difference?

3. Independent Groups design

4. PARTICIPANTS Pairs with highest IQ scores Pairs with next highest IQ scores Pairs with lowest IQ scores Experimental Group - IV: Loud music Control Group – No music Matched Participants design Measure effect on DV Measure effect on DV Is there a difference?

5. Matched Participants design

6. Repeated measures design POPULATION SELECTION SAMPLE Experimental Group - IV: Loud music Control Group – No music ALLOCATION Then Then Control Group – No music Experimental Group - IV: Loud music Measure effect on DV Measure effect on DV Is there a difference?

7. Repeated measures design

8. SCENARIO #1 • A researcher wishes to investigate the effect of alcohol on driving performance. Participants were selected from a group of first year university students. The researcher randomly allocated each participant to one of two groups. The researcher gave all participants three drinks and then asked them to drive a certain course in a driving simulator. The participants in the experimental group were given alcoholic wine while those in the control group were given non-alcoholic wine. The researcher did not inform the participants which drink they received.

9. SCENARIO #2 • An experimenter wishes to investigate the effect of caffeine on the amount of sleep that one gets. She decides to have 20 participants involved in the study. She informs the participants that they will each have to spend 2 nights in a sleep laboratory at Monash University. Their brain activity will be measured so that she can monitor how long they sleep for. She also informs them that they will be given a drink at 9.30pm each night. One night the drink will have caffeine in it and the other night the drink will not have any caffeine in it. The participant will not know when they are to receive the caffeinated drink and not all participants will receive the drinks in the same order.

10. SCENARIO #3 • Professor Raven has developed a new speed-reading technique for primary school children. He wants to test his theory that his speed-reading technique leads to superior comprehension of text than normal reading techniques. He puts the names of 200 Grade 6 students in a bag and randomly allocates each child to one of two groups: Group 1 (speed-reading group) is trained to use Professor Raven’s speed-reading technique and Group 2 (normal instruction group) receives no special training beyond their normal classroom instruction. At the end of the training, all of the children are given a well-known standardised test of reading comprehension. On this test, a higher score indicates better comprehension.

11. SCENARIO #4 • Doctor Fraser is a university research psychologist. His area of expertise is the development of literacy skills in children. Doctor Fraser has designed a new literacy program for Grade 4 children in Victoria. It is a 30-minute television literacy program that runs daily for four weeks. To test this program, Doctor Fraser sent a letter to all parents/guardians of Grade 4 children in Victoria asking for volunteers. The children of the first 100 parents/guardians who replied were accepted into the study. Prior to the experiment, each participant sat a literacy test (Literacy Test A) administered by their Grade 4 teacher. The teachers then sent the results to Doctor Fraser. Participants were put into 50 pairs based on gender and the similarity of their scores on the literacy test (Literacy Test A). A computer program was used to select, by chance, one member of each pair to undertake the literacy program. These participants had to watch the literacy program on television for 30 minutes each day for four weeks. The other member of the pair was allowed to watch cartoons of their choice for 30 minutes per day for four weeks. At the end of four weeks, the participants’ Grade 4 teachers administered a second literacy test (Literacy Test B) and sent the results to Doctor Fraser.

12. Ways to eliminate extraneous variable? • Counterbalancing • Single and double blind procedure • Use of placebos • Standardised testing procedures

13. Counterbalancing to eliminate order effects • Needed to balance out the order effects caused by a repeated measures experimental design. • Counterbalancing involves changing the order of treatments or tasks for participants in a balanced way to counter the biasing influence or unwanted effects on performance.

14. BETWEEN-PARTICIPANTS COUNTERBALANCING RESEARCH QUESTION: Does Alcohol effect driving?

15. WITHIN-PARTICIPANTS COUNTERBALANCING RESEARCH QUESTION: Can people taste the difference between coke and pepsi?

16. Single and double blind procedure • Single blind procedure, participants are ‘blind’ or unaware whether they are in the experimental or control group. Eliminates placebo effects. • Double blind procedure, both the experimenter and the participant are ‘blind’ or unaware whether they are in the experimental or control group. Eliminates placebo effects and experimenter effects.

17. Placebo, or a fake treatment given to control group to mimic the actions of the experimental group. • Standardised instructions should be identical to the way they are carried out to each group.

18. http://www.youtube.com/watch?v=yXiM-nDYzX0phineasgage case study • http://www.youtube.com/watch?v=hHHdovKHDNU observational study • http://www.youtube.com/watch?v=jhSRcTuv2lg interview