This document discusses within-groups or repeated measures designs. In within-groups designs, the same group of participants receives all levels of the independent variable. The key advantages are that all groups are equal at the beginning and the design is very sensitive to changes. Disadvantages include potential carryover effects and sensitivity to time variables like practice and fatigue. Counterbalancing techniques like Latin squares can help control for order effects. Mixed designs combine within- and between-groups approaches to rule out carryover effects while maintaining control. Matched subjects designs aim to reduce error variance by matching and randomly assigning participants.

1. Developmental Research
Methods
Topic 9: Within Groups Designs
10/1/2014 CEDP321 Ryan Sain, Ph.D. 1

2. Within groups designs
 Also called repeated measures
 We are comparing groups of people to
themselves
 Our own best controls
 Each person in every group receives
all levels of the IV

3. Advantages
 All groups are
equal at the
beginning of the
study
 Fewer
participants
 Very sensitive to
changes
(statistically)
◦ Within subject
variance is going
to be low (error
variance)

4. Disadvantages
 Carryover effects
◦ Seeing a picture vs. not seeing one
◦ Permanent change – cannot study in a within
subjects design
◦ Clinical treatments
 Drug trials
 Psychotherapy
 Sensitive to time variables (practice,
fatigue, order of IV)
◦ Order effects and practice effects

5. Counterbalancing
 Complete
counterbalancing
◦ Each condition must
occur with the same
frequency
◦ Each condition must
precede and follow
all conditions an
equal number of
times
 Controls for time
and order effects
 5!

6. Counterbalancing
Group 1 Treat 1 Treat 2 Treat 3
Group 2 Treat 1 Treat 3 Treat 2
Group 3 Treat 2 Treat 1 Treat 3
Group 4 Treat 3 Treat 1 Treat 2
Group 5 Treat 2 Treat 3 Treat 1
Group 6 Treat 3 Treat 2 Treat 1

7. More counterbalancing
 Incomplete counterbalancing
◦ Just balance the order.
Group 1 Treat 1 Treat 2 Treat 3
Group 2 Treat 2 Treat 1 Treat 3
Group 3 Treat 3 Treat 2 Treat 1
 Latin square – doing this randomly with
the number of levels randomized for
each participant
 Differential order effects
◦ certain orders may produce certain outcomes
–
◦ a sort of interaction = treatment x order

8. Mixed designs
 Using
between
groups and
within groups
logic
 Measures change over time within a
group and compares a factor
between groups as well
◦ 2(between factor) x 3 (within factor -
often a time variable)

9. Mixed Designs cont.
 Rule out carryover effects
◦ (using the between groups part)
 High levels of control of a within
design.
 Main effects
◦ Time
◦ Other IV
 Interactions
◦ Time x IV

10. Matched subjects designs
 Reduce error variance
 Combine the benefits of within subjects and
between groups
 Twin studies – not always possible
 Match participants
◦ age, gender, SES, ethnicity, etc.
◦ Then randomly assign one of each match to a
condition.

11. Matching - types
 Use a matched group
as a control group
◦ Random assignment
and equal groups.
 Use a matched group
as an experiment in
unto itself
◦ Two groups matched
◦ Each group has both
males and females –
treat as normal.
 Compare males treatment
to males control, etc

12. Credits
 www.sxc.hu
◦ Mixing table 1 - hovard
◦ Mixing table 2 - riverstorm
◦ People – biewoef
◦ Yin Yang - hisks
◦ Orchids – flajs01
◦ Drugs - alaasafei
 Scrum – www.blackfire.net