Experimental Designs Overview

8/13/2019 Experimental Designs Overview

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An Overview of Experimental DesignRajdeep Chakraborti


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A Classification of Qualitative Research

Procedures

Association

Techniques

Completion

Techniques

Construction

Techniques

Expressive

Techniques

Direct (Nondisguised)

Indirect(Disguised)

Focus Groups Depth Interviews

Projective

Techniques

Qualitative ResearchProcedures


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Causal Research methods Experimentation

Definition of Terms used :

Independent variables are variables or alternatives that aremanipulated and whose effects are measured andcompared, e.g., price levels.

Test units are individuals, organizations, or other entitieswhose response to the independent variables ortreatments is being examined, e.g., consumers or stores.


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Dependent variablesare the variables which measure the

effect of the independent variables on the test units, e.g.,

sales, profits, and market shares.

Extraneous variablesare all variables other than the

independent variables that affect the response of the test

units

Confounding variable: Correlated with both dependent and

independent variable.


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An experiment is formed when a researcher

manipulates one or more independent variables and

measure their effect on one or more dependent

variables while controlling the effect of otherextraneous variables.

ex: store sales and promotion.

Experiments


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Experimental Design

An experimental designis a set of proceduresspecifying

the test units and how these units are to be divided intohomogeneous subsamples,

what independent variables or treatments are to bemanipulated,

what dependent variables are to be measured, and

how the extraneous variables are to be controlled.


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Treatment of independent variable.

Experimental Groups and Control Groups.

Selection and measurement of the dependentvariable (Ex-brand image, brand awareness or

product sales).

Control of extraneous variables.

Issues in Experimentation


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Validity in Experimentation

Internal validity:whether the manipulation of theindependent variables or treatments actuallycaused the effects on the dependent variables.Control of extraneous variables is a necessarycondition for establishing internal validity.

External validity:whether the cause-and-effect

relationships found in the experiment can begeneralized. To what populations, settings, times,independent variables and dependent variables can

the results be projected?


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History: Specific events that are external to theexperiment but occur at the same as the experiment.

Ex-general economy has declined and you do not

get the effect of promo on sales.

Longer the time interval between observations

greater the chance that history will confound the

effect of the experiment.

Categories of extraneous variables


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Maturation: Similar to history, but when ithappens to the test units itself. Hence the changes arenot caused due to the change of the independent

variables, but the test units has changed.

People become older, more experienced, tired andbored.

For store, it could be a change in store layout, dcoretc.



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Testing effect: An effect of testing occurring

when a prior observation affects a later

observation.

ex: Pre-treatment questionnaire making the

respondent familiar with the brand which

results consistent response of the test units.



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Mortality: The respondents are dropping out

of the study.

Dropouts should be distributed evenly in the

sample, not only on high and low score

achievers.



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Experimental environment

LaboratoryExperiments: Contrived setting,Artificial and controlled conditions, control on

influence of extraneous variables (ex: history), high

interval validity, low external validity, time and costless, implementation easy.

Field experiments: Natural setting, no control onexternal variables, low internal validity, high

external validity, time and cost more,

implementation not so easy.


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A Classification of Experimental Designs

Pre-experimental

Designs

One-Shot Study

One Group

Pretest-Posttest

Static Group

True

Experimental

Pretest-Posttest

Control Group

Posttest: Only

Control Group

Solomon Four-

Group

Quasi

Experimental

Time Series

StatisticalDesigns

Completely

Randomised

Randomised

Blocks

Latin Square

Factorial Design

Experimental Designs


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Notations used in Experimentation

X = Exposure of a group to an experimental treatment orindependent variable

O = Observation or measurement of the dependentvariable on the test units O1, O2, O3 etc.)

R = Random assignment of test units to experimental groups

EG = experimental group which is assigned to experimentaltreatment

CG = control group of test units involved in the experiment.

This group is not exposed to experimental treatment

Note that the notation used in experimental design assumes atime flow from left to right


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Pre-Experimental Designs

One-shot design

EG: X O1

Example: Impact of sales promotion on sales in select

supermarkets

Disadvantages: (i) The test units are not selected randomly

(ii) Various extraneous variables may influence the dependent

variable including history, maturation.Used for exploratory research rather than conclusiveresearch


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One-group pre-test-post-test design

EG: O1 X O2

TE = O2O1

Example: Impact of training program on

employee productivity.

Extraneous variables are uncontrolled.


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Static Group Design

EG: X O1

CG: O2

TE = (O1- O2)

Two groups of test units are involved in the experiment

the experimental group and the control group

Influence of various extraneous variables such as1. Selection bias (Non random selection of test units)

2. Mortality effect ( Test units may drop out )


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Solomon Four Group DesignExperimental Group 1: R O1 X O2Control Group 1: R O3 O4Experimental Group 2: R X O5

Control Group 2: R O6

Note:Use this design when it is suspected that, in taking a

test more than once, earlier tests have an effect on later tests,

for example by learningorprimingeffects.

For a reliable result, several sets of four tests should be applied and the means used.


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Quasi-experimental designsresult when the researcher isunable to achieve full manipulation of scheduling or allocationof treatments to test units but can still apply part of theapparatus of true experimentation

example:To perform an educational experiment, a class mightbe arbitrarily divided by alphabetical selection or by seatingarrangement.

time series designs.

01 02 03 04 05 X 06 07 08 09 010

There is no randomization of test units to treatments.

The timing of treatment presentation, as well as which testunits are exposed to the treatment, may not be within theresearcher's control.


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A statistical designis a series of basic experiments thatallows for statistical control and analysis of externalvariables:

completely randomized design

randomized block design

Latin square design

factorial designs.


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Completely Randomized Design

Evaluating the effect of a single variable Effect of extraneous variable controlled using the

randomization technique

EG1: R X1 O1EG2: R X2 O2EG3: R X3 O3

Effect on sales of coffee when product is kept inthree levels of shelf height (knee level, waist leveland eye level).


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Randomized Block Design

A statistical design in which the test units are blocked on the

basis of external variable to ensure that various experimental

and control groups are matched closely on that variable.

Used when one extraneous variable may influence

experimental results. Store size while measuring effect of

promo on sales.

Test units are blocked or grouped based on the extraneous

variables.


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Factorial Design

A statistical experimental design that is used to

measure the effect of two or more independent

variables in various levels and allow the interaction

between the variables.

Two levels of kindependent variables.

Two effects can be determined-the main effect and

the interaction.


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Latin square design

Two blocking effects i.e two non interacting extraneousvariables

Example: Impact of different pricing schemes on sales will be

influenced by store patronage and POP display

Always a square designlevels of all factors are same

Interaction effect cannot be measured


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Thank You!

Documents

Experimental Designs Overview