This document outlines various experimental designs used in research. It describes laboratory and field experiments, randomized designs like completely randomized designs and randomized block designs. It discusses internal and external validity and introduces key terms like the independent and dependent variables. It also explains threats to validity from extraneous variables and outlines different types of experimental designs from pre-experimental to true experimental designs and factorial designs. It provides an example of a 2x2 factorial design and describes Latin square designs.

1. Experimental Designs

2. • Laboratory experiment- researcher creates a
situation with the desired condition and then
manipulates some variables while controlling
others.
• A field experiment is a study in a realistic or
natural setting and involves manipulation of
the independent variable while carefully
controlling the others

3. Randomized designs
• Completely Randomized Designs (CRD)- an
experimental design that uses a random
process to assign experimental units to
treatments
• A Randomized Block Design- Grouping test
units into homogenous blocks (similar to
stratified sampling)

4. Validity
• Internal validity: Is the effect due to our
hypothesized cause?
• External validity: Can we generalize to other
samples?

5. Experimental designs
• X refers to the exposure of the subject to an
experimental treatment
• O refers to the process of observation and
measurement of the test units
Eg: X O1 O2

6. Extraneous variables
• History- specific events external to the
experiment but occurring at the same time ,
that may affect the criterion variable
• Maturation-Changes occurring within test
units that are not due to the experimental
variable but due to the passage of time
• Testing-the experiment itself may affect the
responses

7. • Instrument variation- changes in the
instrument may account for the differences
• Statistical regression-the tendency of the
extreme cases to move closer to the average
during the course of the experiment
• Selection bias- the way in which the test units
are selected

8. Pre experimental design
• One shot case study: X O
• One group pretest-post test design: O1 X O2
• Static group comparisonEG X O1
CG
O2
No way of ensuring the two groups are
equivalent prior to the comparison

9. True experimental designs
• Before-After with control group design
EG: (R) O1 X O2
CG: (R ) O3
O4
The difference between O3 and O4 reflects external causes.
But they would exert a similar influence on EG also
O2-O1= E+U
O4-O3= U
Design is nearly ideal. Accounts for all external causes except
Interactive testing. So strictly:
O2-O1=E+U+I
O4-O3= U

10. Four group- six study design
•
•
•
•
EG 1:
CG 1:
EG 2:
CG 2:
O1 X O2 O2-O1 = E+U+I
O3
O4 O4-O3= U
X O5 O5- ½ (O1+O3)= E+U
O6 O6- ½ (O1+O3)= U

11. Time series experimental designs
• Several observations taken before the
treatment; then the treatment (X) is
administered, then several observations are
taken to measure if there is a change in the
pattern after as compared to before the
experiment
• O1 O2 O3 X O4 O5 O6

12. Factorial designs
• Allow for the testing of two or more treatments (factors) at
various levels.
• Main effect: the influence on a dependant variable by each
independent variable separately
• Interactive effect: the effect on a dependant variable by
combinations of two or more independent variables
• Interactive effects may be more than the total of the main
effects

13. • A researcher wants to understand the
influence of both gender and the
advertisement (2 advts are beingconsidered)
on ‘believability’. There are 2 independent
variables: gender and advt.
• Each variable has 2 levels (2 advts and 2
genders)- leads to a 2X2 factorial design

14. Latin square design
• Attempts to control or block out the
confounding effect of extraneous factors.
• A balanced two-way classification scheme
• In a Latin square design, both the confounding
factors must have the same number of levels
• Eg: A taste test involving 3 levels of tastes
administered to 3 different people with the
order of the administration randomized