4: Experimental research within subjects

Question 1

selection

Answer 1

-a confound where systematically different

types of subjects are exposed to each level of the IV

Question 2

within subjects design

Answer 2

-designs eliminate selection effects altogether
by exposing every subject to all levels of the IV (each subject serves as their own control)
• Concurrent-measures or repeated-measures

Question 3

concurrent measures

Answer 3

• present all levels of the independent variable to one group at the same time
  • Preference is often measured

Question 4

repeated measures

Answer 4

-designs expose every participant to all levels of the independent variable sequentially

Question 5

repeated measures design setup

Answer 5

• the same subjects are used in all conditions
  • Subjects are randomly assigned to treatment or condition orders

-related to matched group, taken to the extreme

-Evaluate changes in behavior within subjects across multiple treatments or conditions
• Sometimes called simply within-subjects

Question 6

carryover in repeated measures

common sources:

Answer 6

-occurs when later responses of the subject are
systematically affected by their earlier responses

-practice: in earlier treatments may enhance performance in later treatments
-fatigue may impair performance
-contrast: subjects may compare treatments to previous
treatments, which may affect behavior
-contamination: occurs when later responses of the subject are systematically affected by their earlier responses

-unbalanced carryover may lead to order effects

Question 7

dealing with order effects:

Answer 7

-steps to minimize carryover
• Pre-training or practice
• Rest periods between treatments
• Blind design and/or concealing differences

-Counterbalancing balances

Question 8

counterbalancing

Answer 8

• The various conditions are presented in a different order for different subjects
• Subjects randomly assigned to one of the treatment orders
• Attempts to evenly distribute carryover among conditions, eliminating order effects as potential confounds

Question 9

counterbalancing techniques

Answer 9

• Full (complete) counterbalancing: equal numbers of
  subjects randomly assigned to every possible ordering of conditions

-Partial counterbalancing: equal numbers of subjects
randomly assigned to only some of the possible orders of conditions

-Pseudo
random ordering: each subject receives multiple exposures to each condition, interleaved in a
pseudorandom order

Question 10

pros within subject designs

Answer 10

-Avoids selection effects from nonequivalent groups

-Greater statistical power (more likely to detect an effect)
• Evaluating changes in DV within subjects eliminates error variance due to individual differences

-Fewer subjects required

Question 11

cons within subject

Answer 11

• More demanding on subjects
• Subject attrition is a problem, especially if multi-session

-Carryover: Exposure to a previous treatment may affect
DV/behavior in a subsequent treatment, a potential
confound as order effect
• Controlled for with counterbalancing
• Counterbalancing may sometimes be impossible or impractical due to permanent/irreversible changes or asymmetrical carryover