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within groups research in psychology
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04/10/2023 CEDP321 Ryan Sain, Ph.D. 1
Developmental Research MethodsTopic 9: Within Groups Designs
Within groups designsAlso called repeated measuresWe are comparing groups of
people to themselvesOur own best controlsEach person in every group
receives all levels of the IV
AdvantagesAll groups are
equal at the beginning of the study
Fewer participantsVery sensitive to
changes (statistically)◦Within subject
variance is going to be low (error variance)
DisadvantagesCarryover 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
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!
Counterbalancing
Group 1 Treat 1 Treat 2 Treat 3
Group 3 Treat 1Treat 2 Treat 3
Group 2 Treat 1 Treat 2Treat 3
Group 4 Treat 1 Treat 2Treat 3
Group 5 Treat 1Treat 2 Treat 3
Group 6 Treat 1Treat 2Treat 3
More counterbalancing Incomplete counterbalancing
◦ Just balance the order.
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
Group 1 Treat 1 Treat 2 Treat 3
Group 2 Treat 1Treat 2 Treat 3
Group 3 Treat 1Treat 2Treat 3
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)
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
Matched subjects designsReduce error varianceCombine the benefits of within subjects and
between groupsTwin studies – not always possibleMatch participants
◦ age, gender, SES, ethnicity, etc.◦ Then randomly assign one of each match to a
condition.
Matching - typesUse 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
Creditswww.sxc.hu
◦Mixing table 1 - hovard◦Mixing table 2 - riverstorm◦People – biewoef◦Yin Yang - hisks◦Orchids – flajs01◦Drugs - alaasafei
Scrum – www.blackfire.net