Business Research Methods William G. Zikmund

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Business Research MethodsWilliam G. Zikmund

• Chapter 12
• Experimental Research

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Experiment

• A research investigation in which conditions are
  controlled
• One independent variable is manipulated
  (sometimes more than one)
• Its effect on a dependent variable is measured
• To test a hypothesis

3
Basic Issues of Experimental Design

• Manipulation of the Independent Variable
• Selection of Dependent Variable
• Assignment of Subjects (or other Test Units)
• Control Over Extraneous Variables

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The experimenter has some degree of control over
the independent variable. The variable is
independent because its value can be manipulated
by the experimenter to whatever he or she wishes
it to be.
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Experiment Treatment

• Alternative manipulations of the independent
  variable being investigated

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Independent Variable

• The experimenter controls independent variable.
• The variables value can be manipulated by the
  experimenters to whatever they wish it to be.

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Manipulation of Independent Variable

• Classificatory Vs. continuous variables
• Experimental and control groups
• Treatment levels
• More than one independent variable

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Experimental Treatments

• The alternative manipulations of the independent
  variable being investigated

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Dependent Variable

• Its value is expected to be dependent on the
  experimenters manipulation
• Criterion or standard by which the results are
  judged

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Dependent Variable

• Selection
• e.g... sales volume, awareness, recall,
• Measurement

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Test Units

• Subjects or entities whose response to the
  experimental treatment are measured or observed.

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Two Types of Experimental Error

• Constant errors
• Random errors

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Field versus Laboratory Experiments
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Establishing Control
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• Physical Control
• Holding the value or level of extraneous
  variables constant throughout the course of an
  experiment.
• Statistical Control
• Adjusting for the effects of confounding
  variables by statistically adjusting the value of
  the dependent variable for each treatment
  conditions.
• Design Control
• Use of the experimental design to control
  extraneous causal factors. Eg. Demand

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Demand Characteristics

• Experimental procedures that intentionally hint
  to subjects something about the experimenters
  hypothesis

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Demand Characteristics

• Guinea pig effect
• Hawthorne effect

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Field Vs. Laboratory Experiment
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Laboratory Experiment
Field Experiment
Artificial-Low Realism
Natural-High Realism
Few Extraneous Variables
Many Extraneous Variables
High control
Low control
Low Cost
High Cost
Short Duration
Long Duration
Subjects Aware of Participation
Subjects Unaware of Participation
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Control Groups

• Isolate extraneous variation

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When does an Experiment have Internal Validity?

• Internal Validity - The ability of an experiment
  to answer the question whether the experimental
  treatment was the sole cause of changes in a
  dependent variable
• Did the manipulation do what it was supposed to
  do?

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Factors Influencing Internal Validity

• History
• Maturation
• Testing
• Instrumentation
• Selection
• Mortality

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Isolating Extraneous Variationwith a Control
Group

• History Effects
• Maturation Effects
• Mortality Effects

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Type of Extraneous Variable
Example
History - Specific events in the environment
between the Before and After measurement that are
beyond the experimenters control Maturation -
Subjects change during the course of the
experiment Testing - The Before measure
alerts or sensitizes subject to nature of
experiment or second measure.
A major employer closes its plant in test market
area Subjects become tired Questionnaire about
the traditional role of women triggers enhanced
awareness of women in an experiment.
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New questions about women are interpreted differen
tly from earlier questions. Control group and
experimental group is self-selected group based
on preference for soft drinks Subjects in one
group of a hair dying study marry rich widows
and move to Florida
Instrument - Changes in instrument result in
response bias Selection - Sample
selection error because of differential selection
comparison groups Mortality - Sample
attrition some subjects withdraw from experiment
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How can Internal Validity Increase?
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Increasing Internal Validity

• Control group
• Random assignment
• Pretesting and posttesting
• Posttest only

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What are the Different Basic Experimental Designs?
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Quasi-Experimental Designs

• One Shot Design (After Only)
• One Group Pretest-Posttest
• Static Group Design

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One Shot Design (After Only) X O1
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One Group Pretest-Posttest O1 X O2
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Static Group Design Experimental Group X O1
Control Group O2
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Three Good Experimental Designs

• Pretest - Posttest Control Group Design
• Posttest Only Control Group
• Solomon Four Group Design

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Pretest-Posttest Control Group Design
Experimental Group R O1 X O2 Control
Group R O3 O4
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Posttest Only Control Group
Experimental Group R X O1 Control
Group R O2
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One-Shot DesignInternal Validity Problems

• History
• weak
• Maturation
• weak
• Testing
• not relevant

• Instrumentation
• not relevant
• Selection
• weak
• Mortality
• weak

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One-Group Pretest-PosttestInternal Validity
Problems

• History
• weak
• Maturation
• weak
• Testing
• weak

• Instrumentation
• weak
• Selection
• controlled
• Mortality
• controlled

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Static-Group DesignInternal Validity Problems

• History
• controlled
• Maturation
• possible source of concern
• Testing
• controlled

• Instrumentation
• controlled
• Selection
• weak
• Mortality
• weak

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Pretest-Posttest ControlInternal Validity
Problems

• History
• controlled
• Maturation
• controlled
• Testing
• controlled

• Instrumentation
• controlled
• Selection
• controlled
• Mortality
• controlled

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Solomon Four-Group DesignInternal Validity
Problems

• History
• controlled
• Maturation
• controlled
• Testing
• controlled

• Instrumentation
• controlled
• Selection
• controlled
• Mortality
• controlled

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Posttest-Only ControlInternal Validity Problems

• History
• controlled
• Maturation
• controlled
• Testing
• controlled

• Instrumentation
• controlled
• Selection
• controlled
• Mortality
• controlled

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Solomon Four Group Design
Experimental Group 1 R O1 X O2 Control
Group 1 R O3 O4 Experimental Group
2 R X O5 Control Group 2 R
O6
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Advanced Experimental Designs are More Complex

• Completely randomized
• Randomized block design
• Latin square
• Factorial

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Completely Randomized Design

• An experimental design that uses a random process
  to assign subjects (test units) and treatments to
  investigate the effects of only one independent
  variable.

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Completely Randomized Designs
Control no music
Experimental treatment slow music
Experimental treatment fast music
Average minutes shopper spends in store
16 18 12
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Independent Variable A
Level 1
Level 2
Level 3
Group A
Group B
Group C
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Completely Randomized Design
With a pretest posttest
Group A R O1 X1 O2 Group B R O3 X2 O4 Group
C R O5 X3 O6
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Completely Randomized Design
With a posttest
Group A R X1 O1 Group B R X2 O2 Group
C R X3 O3
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Randomized Block Design

• An extension of the completely randomized design
  in which a single extraneous variable that might
  affect test units response to the treatment has
  been identified and the effects of this variable
  are isolated by blocking out its effects.

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Randomized Block Design
Independent Variables
Control no music
Experimental treatment slow music
Experimental treatment fast music
Mornings and afternoons Evening hours
Blocking variable
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Factorial Design

• An experiment that investigates the interaction
  of two or more variables on a single dependent
  variable.

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Independent Variable 1
Slow Music
Fast Music
No Music
No Music cart signs
Independent Variable 2
Grocery cart signs
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Factorial Design -- Roller Skates
Package Design
Price Red Gold 25 Cell 1 Cell 4 30 Cell
2 Cell 5 35 Cell 3 Cell 6
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Effects

• Main effect
• The influence of a single independent variable on
  a dependent variable.

• Interaction effect
• The influence on a dependent variable by
  combinations of two or more independent variables.

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2 x 2 Factorial Design
Ad A Ad B
Men Women
65 65
Main Effects of Gender
gt
70 60
gt
Main Effects of Ad
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Interaction Between Gender and Advertising Copy

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Independent Variable 1
Level 1 Level 2
Level 1 Level 2
Group A
Group B
Independent Variable 2
Group D
Group C
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2 x 2 Factorial with a Pretest Posttest
Group A R O1 X11 O2 Group B R O3 X21 O4 Group
C R O5 X12 O6 Group D R O7 X22 O8
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2 x 2 Factorial Design with a Posttest Measure
Group A R X11 O1 Group B R X21 O2 Group
C R X12 O3 Group D R X22 O4
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A Test Market Experiment on Pricing
Sales in Units (thousands)
Regular Price .99 130 118 87 84 X1104.75 X119
.58
Reduced Price .89 145 143 120 131 X2134.75
Cents-Off Coupon Regular Price 153 129 96 99 X1
119.25
Test Market A, B, or C Test Market D, E, or
F Test Market G, H, or I Test Market J, K, or
L Mean Grand Mean
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Latin Square Design

• A balanced, two-way classification scheme that
  attempts to control or block out the effect of
  two or more extraneous factors by restricting
  randomization with respect to the row and column
  effects.

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1 2 3 1 A B C 2 B C A 3 C A B
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