ch8(1)1 Within Subjects (Participants) Designs All participants serve in each condition of the study. Advantage: Individual Differences are not a Confound.

Types of WS Designs 1) Pre-Post Design with no treatment control group. Used when the purpose is show a change between conditions (i.e. treatment or an outcome) and the order of the conditions is logically set (i.e., pre test must proceed post test). ch8(1)2

2)WS design with counterbalancing for order. Used when comparing conditions and the conditions can be measured in any order. Weakness: Sequencing Effects: Participation in one condition may effects participation in a subsequent condition(s). ch8(1)3

4 A) Order Effects Changes in performance due to practice, familiarity, boredom that are due to repeated testing and not to differences in the IV.

ch8(1)5 B)Carry-over Effects Long-lasting effects participation in one condition that carry-over to effect performance in subsequent conditions. e.g., Learning, Expectation, attitude, physical changes due to experimental condition. E.g., Reward Contrast effects in Rats

ch8(1)6 Example of Carry Over effects: Reward Contrast effects in Rats

ch8(1)7 Controlling for Sequence Effects (WS Design) 1) Counterbalance - controls for order effects and for unexpected carry-over effects. Counterbalancing: Within your study, each condition occurs equally as often in each ordinal position, and each condition occurs equally as often before and after each other condition.

ch8(1)8 Randomized Counterbalancing Each Subject gets a different order. ABC ACB BCA BAC CAB CBA Subjects are randomly assigned to order conditions.

Complete Randomized Counterbalancing All possible orders of conditions are used in and participants are randomly assigned so that there are equal numbers in each order condition. ch8(1)9

Equal numbers of subjects are assigned to each order condition, thus order effects are controlled by equalling the effects of order for each condition. Condition ACondition BCondition C 1st2nd3 rd 1st3rd2 nd 3rd1 st 2nd1st3 rd 2nd1 st 3rd1st2 nd ch8(1)10

Incomplete Counterbalancing With 4 conditions all orders would total 24. ABCD BACDCABDDABC ABDCBADCCADBDACB ACBDBCADCBADDBAC ACDBBCDACBDADBCA ADABBDACCDABDCAB ADBABDCACDBADCBA ch8(1)11

Rules for Incomplete Counterbalancing 1)Each condition must appear an equal number of times in each ordinal position. 2)Each condition must precede and be followed by every other condition equal numbers of times. ch8(1)12 ABDC BCAD CDBC DACB

ch8(1)13 Intrasubject counterbalancing Each subject gets each possible order. ABCCBA

ch8(1)14 Between Subjects Designs – Each participant serves in only one condition in the study. Confound: Individual Differences

ch8(1)15 Control of Individual Differences e.g., IQ, personality, sex, race, age etc. Random Assignment - Each member of the sample has an equal chance of being assigned to any of the conditions.

Power Ability to find a difference between conditions when a difference actually exists. When designing a study we want high power!! ch8(1)16

Power and Designs 1)WS designs have higher power than BS designs and should ALWAYS be considered first. ASK Can I counterbalance for order? If yes, then counterbalance. If no, use pre-post test with no-treatment control group. ch8(1)17

BS designs are used only when participants cannot be in more than one condition of the study. Being in each condition permanently changes a person so that they cannot be in other conditions of the study. ch8(1)18

Comparison between treatment types here is a BS comparison ch8(1)19 PrePostChange Cognitive Therapy Drug treatment Combined Treatment No treatment Control

BS designs are commonly used for Natural Manipulation studies (e.g., sex differences, personality differences). These are not experiments and they have low Internal Validity. ch8(1)20