PSYC 200W Lecture Notes - Lecture 13: Factorial Experiment, Pocket Cube, Random Assignment
28 Jun 2018
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One-Way Designs
Only one IV is manipulated
Simplest one-way design - two-group experimental design where there are 2 levels of IV
At least 2 conditions required for experiment
Assign participants to conditions - randomized, matched-subjects, and repeated measures
3 ways to assign participants to conditions - simple random design, matched participant
design/sample, within participants design
oThese 3 random assignment designs are called posttest-only design because the DV is
measured only after the experimental manipulation has occurred
Pretest-posttest design - DV is measured twice - once before IV is manipulated and once after
oDo not always need pretest and posttest because if researcher assigned the participants
using 1 of the 3 conditions, then the experiment and control group should be pretty
equivalent and only posttest can be used to study IV effects
Advantages of pretest-posttest:
oBy obtaining pretest scores on DV, researchers can verify that the participants did not
differ with respect to DV before the experiment
oBy comparing pretest and posttest scores, researchers can see how much the IV
changed the participant's behavior - pretest provides baseline data
oThey are more powerful - more likely to detect effects of IV on DV. This is because
variability in pretest scores can be removed before examining effects of IV
Disadvantages of pretest-posttest:
oPretests can lead to pretest sensitization and participants might respond to IV
differently than they would have
oEven if they don't sensitize, they cue the participant about the hypothesis and lead to
demand characteristics
Factorial Designs
2 or more independent variables are manipulated and they have to have 2 or more levels
When we have 2 IV with 2 levels each - We call it 2x2 factorial design = _ x _
# of blanks = # of IV and the number in the blank = no. of levels
Levels = # of values of a single IV can take on -
Condition = total # of experimental groups (taking into account ALL IV's & levels) -
2x2 (2 IV, 2 levels) = 4 conditions
3x3 (2 IV, 3 levels) = 9 conditions
2x2x2 (3 IV, 2 levels) = 8 conditions
3x2 (2 IV, one IV has 3 levels and second IV has 2 levels) = 6 conditions
IV1 = Meditation
IV2 = Presence of others
DV = stress
2x3 factorial design = 6 conditions
Assignment of participants to conditions - includes the 3 designs - randomized, matched-
subjects, and repeated measures
Another type of condition assignment is mixed factorial design
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Simplest one-way design - two-group experimental design where there are 2 levels of iv. At least 2 conditions required for experiment. Assign participants to conditions - randomized, matched-subjects, and repeated measures. 3 ways to assign participants to conditions - simple random design, matched participant design/sample, within participants design o. These 3 random assignment designs are called posttest-only design because the dv is measured only after the experimental manipulation has occurred. By obtaining pretest scores on dv, researchers can verify that the participants did not differ with respect to dv before the experiment o. By comparing pretest and posttest scores, researchers can see how much the iv changed the participant"s behavior - pretest provides baseline data o. They are more powerful - more likely to detect effects of iv on dv. This is because variability in pretest scores can be removed before examining effects of iv.
