Finish Chapter 7 and Review

10/25/2012

It’s that time in the semester…

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Roadmap

• Review of last class• Exam #3: Tuesday– Format: MC, short answer

• Finish Ch. 7 (control techniques)• Review “muddiest points”

Announcement

• Workshop: Graduate School in Psychology• When: Monday, 10/29, 1-2pm• Where: Terrill Hall 281• Who: Dr. Barnett

• Topics:– Types of graduate programs there are– The application process– Things you can do throughout your undergraduate career

to increase your competitiveness for graduate programs

Review:

• Control during the experiment– Counterbalancing within-participants

designs

– Controlling for participant effects– Controlling for experimenter effects

Counterbalancing

• Used to control for sequencing effects in a repeated measures (aka within-subjects) design

• Sequencing effects occur when participants participate in more than one condition

• Two types of sequencing effects– Order effect– Carryover effect

Counterbalancing Techniques

• Randomized counterbalancing• Intrasubject counterbalancing

• Complete counterbalancing• Incomplete counterbalancing

individual

group

Counterbalancing

• Order effect– “Arises from the order in which treatment

conditions are administered to participants”– Treatment/experiment exposure can influence

performance on subsequent tasks and measures– Most common:• Practice effect• fatigue

Counterbalancing

• Carryover effect– Performance in one condition is affected by the

condition that precedes it– Example: Participant receives active drug before

the placebo, and the residual effects are still present during placebo condition

• One strategy: “wash-out” period

Types of Counterbalancing

• Randomized counterbalancing– Sequence order is randomly determined for each

individual– Just like random assignment to conditions– You do not decide the sequence, must use a random process to decide

order

Types of Counterbalancing

• Intrasubject Counterbalancing– When each participant receives all levels of the IV

more than one time– Have participants take conditions first in one

order, then again in the reverse order

– Disadvantage: Participant burden is increased• Must complete each condition more than once

Types of Counterbalancing

• Complete and Incomplete counterbalancing– Group counterbalancing– Determine possible sequences– Randomly assign to sequence such that sequences

are distributed across groups rather than individuals

Participant Effects

• Demand characteristics– Cues in the experiment that might influence

participant behavior

• Positive self-presentation– Motivation for participants to present themselves

in a positive light

Control of Participant Effects

• Deception– Giving participants a bogus rationale for the

experiment

• Can range from minor deceit to more elaborate schemes

Classic example: Milgram studies

Control of Participant Interpretation

• Previously discussed methods provide good control for demand characteristics of study

• But how do we know what participants’ perceptions of our study are?– Ask them!

Control of Participant Interpretation

• Retrospective Verbal Reports: after experiment– Disadvantage: Participants might forget

perceptions by the end of the study

• Concurrent Verbal Reports: during experiment– Solomon’s Sacrifice Groups– Concurrent probing– Think-aloud technique

Control of Experimenter Effects

• Experimenter effects– The biasing influence that can be exerted by the

experimenter

• Data Recording errors--control– Be careful– Multiple observers and data recorders– Keep experimenter blind to participants’ conditions– Electronic or mechanical data recording*

Control of Experimenter Effects

• Experimenter Attribute Errors– Some experimenters, because of their attributes,

produce more of an effect than other experimenters

• Control technique:– Experimenters should run all conditions– Experimenters same on characteristics that might

affect DV

Control of Experimenter Effects

• Experimenter Expectancy Errors– Experimenter’s expectations about the study

influence participant responses

Control techniques:• Blind technique• Partial blind technique• Automation

Ideal:Control Participant AND Experimenter Effects

• Double-Blind Placebo Method– Participant and experimenter blind to condition– “Devise manipulations that appear essentially

identical to research participants in all conditions”– Example: Compare drug to identical sugar pill

(placebo)

Review: Muddiest Point(s)

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different experimental designs - examples

Types of counterbalancing

factorial design and ANOVA

yoked control - human example

which statistical test to use

order effect and carryover effect

matching participants

interaction vs. main effect

"visual representations"

weak vs. strong experimental designs

within-participant design vs. between-participants

visual data displays

"control" and uses of the term

strengths and weaknesses of experiemental designs

0 2 4 6 8 10 12 14 16 18 20

Muddiest Point

A note

• Choosing the correct statistical test for a study– Not on this exam, but it’s coming up– Just practicing for now

Experimental Designs

• Weak vs. Strong– Differences?

• Between-participants vs. within-participants

• Let the name guide you– (E.g., one-group, posttest-only)– Is is a weak or a strong design? What information

do you get from the design?

Let’s try some examples

1. You want to examine the impact of the use of PowerPoint slides in class on class attendance in male and female students. Students are randomly assigned to a psychology class with low, moderate, or high use of PPT slides.– IV(s)– DV– Strong or weak?– Between or within?– Which type of research design?

Data for Example 1.

PowerPoint Use0

10

20

30

40

50

60

70

80

Male Female

What effects do we see?Is there a main effect of gender on class attendance?Is there a main effect of PPT use on class attendance?Is there an interaction effect of gender and PPT use on class attendance?

Example 22. Bob wants to know if nicotine patches really help people quit

smoking. He identifies 100 people who have smoked at least a pack per day for 10 years or more and who want to quit. Bob randomly assigns participants to either wear a nicotine patch for 1 month or to not wear a patch. At the end of the month, participants are asked how many cigarettes they smoke daily.– IV(s)– DV– Strong or weak?– Between or within?– Which type of research design?

Data for Example 2# CPD pre- #CPD post-

Nicotine Patch 20 2

No Patch 20 18

Tutorial on Factorial Design

• Interactive, walks through and explains• Several examples• Quizzes throughout to test yourself• http://teachpsych.org/otrp/resources/factoria

l/index.php

Example 3

• A group of psychologists are testing a new therapy with a group of clients experiencing complex grief after the death of a partner. They obtain patient ratings of grief, administer the new therapy for 6 weeks, and then obtain grief ratings again. They find that the mean grief rating is 10 points lower after completion of the new therapy.

• This is an example of which experimental design?• Why?• Is this a weak or strong design? Why?– What would make it a stronger design?