Chapter 9
Control Techniques
♣
Back to Brief Contents

Introduction 

Randomization 

Matching 

Counterbalancing 

Control of Participant Effects 

Control of Experimenter Effects 

Likelihood of Achieving Control
9.0 Introduction
Back to Chapter Contents

Goal of experimentation ― identify the causal
effect of the IV
 Must have internal validity to do this
 Internal validity requires control of confounding
variables

Ways of achieving control
— Design of the experiment
— Statistical adjustments
— Incorporate control techniques into the research
design
9.1 Randomization
-1
Back to Chapter Contents



Randomization is a statistical control technique
to equate groups of participants
This is the most important and basic control
technique
Random selection —selecting people at random
from a defined population


Insures that the sample selected is representative of the
population
representative: sample P have the same characteristics
as the people in the population
Studies seldom if ever do this because of expense, etc
9.1 Randomization
-2
Back to Chapter Contents

Random assignment —randomly assigning
participants to treatment groups

Provides maximum insurance that groups are equal

Equates groups because every person has an equal
chance of being assigned to each group

Accomplishes this by randomly distributing the
extraneous variables over the treatment groups
Fig 9.1 Tab 9.1
9.1 Randomization
-3(end)
Back to Chapter Contents

Random Assignment Exercise


Randomly assign 40 children to four different drug
conditions using the table of random numbers in
appendix D
Exhibit 8.1 1 2
Logon to www.randomizer.org and use the
randomizer in this site to randomly assign 40 children
to the four drug conditions
9.2 Matching
-1
Back to Chapter Contents


Uses of any of a variety of techniques to equate
participants in the treatment groups on specific
variables
Advantages of matching


Controls for the variables on which participants are
matched
Increases the sensitivity of the experiment
9.2 Matching
-2(end)
Back to Chapter Contents

Matching by Holding Variables Constant 

Matching by Building the Extraneous Variable into the
Research Design 

Matching by Yoked Control 

Matching by Equating Participants 
9.2.1 Holding Variables Constant
Back to Chapter Contents

Matches on the variable held constant
Fig 9.2

Disadvantages

Restricts the population size

Restricts generalization to the type of participants in
the study
9.2
9.2.2 Building EV into Research Design
Back to Chapter Contents

Should be used only when you are interested in the
effect of the effect of the extraneous variable
Fig 9.3
9.2
9.2.3 Matching by Yoked Control
Back to Chapter Contents

Controls the temporal relationship between an
event and a response

Brady (1958)



Emotional stress → Ulcer
Stress: Press a lever every 20-sec to avoid shock
Control: receive the same temporal sequence of shock
9.2
9.2.4 Matching by Equating Participants
Back to Chapter Contents

Precision control —match case by case Fig 9.4

Disadvantages




Identifying the variables on which to match
Matching increases as the number of variables on which
to match increases
Some variables difficult to match
Frequency distribution control —match on the
overall distribution of the selected variables Fig 9.5

Disadvantage

Combination of variables may be mismatched
(e.g.) Age-IQ: (E) Old-high IQ, Young-low IQ
(C) Old-low IQ, Young-high IQ
9.2
9.3 Counterbalancing
Back to Chapter Contents

Used to control sequencing effects

Type of Sequencing effects

Fig 9.6
Order effect Tab 9.2
arising from the order in which the treatment conditions are
administered to P

Carry-over effect Tab 9.3
occurs when performance in one treatment condition affects
performance in another treatment condition

Counterbalancing procedures

Intrasubject Counterbalancing: The ABBA technique 

Intragroup Counterbalancing 
9.3 Counterbalancing - intrasubject
Back to Chapter Contents

Intrasubject or ABBA technique — counterbalances
on a case-by-case basis

Controls only for linear sequencing effects Tab 9.4

Nonlinear order effects can be controlled if you use the
ABBA plus BAAB counterbalancing Tab 9.5

Can’t control nonlinear carry-over effects
9.3 ◄
9.3 Counterbalancing – Intragroup
-1
Back to Chapter Contents

Intragroup Counterbalancing
(e.g.) ABC ACB BAC BCA CAB CBA

Incomplete Counterbalancing (Latin square)
Participant
1
2
3
4
Sequence
A B D C
B C A D
C D B A
D A C B
9.3 ◄
9.3 Counterbalancing - Intragroup
-2
Back to Chapter Contents

Intragroup Counterbalancing

Incomplete Counterbalancing (Latin square)
A
B
C
D
E
B
C
D
E
A
E
A
B
C
D
C
D
E
A
B
D
E
A
B
C
D
E
A
B
C
C E
D A
E B
A C
B D
B
C
D
E
A
A
B
C
D
E
9.3 ◄
9.3 Counterbalancing - Intragroup
-3(end)
Back to Chapter Contents

Intragroup Counterbalancing

Incomplete Counterbalancing (Latin square)
1,2,n,3,(n-1),4,(n-2),5,…
2,3,n+1,4,…
(e.g.) A
B
C
D
E
F
B F C E
C A D F
D B E A
E C F B
F D A C
A E B D
D
E
F
A
B
C
( p. 282, 283 )
9.3 ◄
9.4 Control of Participant Effects
-1
Back to Chapter Contents

Double Blind Placebo Model



Participants, Experimenter
Blind: the treatment condition administered to P
Deception ― giving the P a bogus rationale for the
experiment

provide hypothesis : unrelated or orthogonal; false but
plausible
9.4 Control of Participant Effects
-2(end)
Back to Chapter Contents

Perceptual Control, or Control of Participant
Interpretation

Retrospective verbal report


postexperimental inquiry
Concurrent verbal report

sacrifice groups: stopped at a different point

concurrent probing: at the end of each trial

think-aloud technique
9.5 Control of Experimenter Effects
-1
Back to Chapter Contents


Control of Recording Errors

Aware of the necessity: ensure the accuracy

Kept blind

Mechanical or electronic device
Control of Experimenter Attribute Errors

Interact with treatment effect?

Minimize: Control Attributes that correlate with DV
Tab 9.6
9.5 Control of Experimenter Effects
-2(end)
Back to Chapter Contents

Control of Experimenter Expectancy Error

The Blind Technique

The Partial Blind Technique

Automation