1.
EXPERIMENTAL DESIGNS
COMPLETELY RANDOMIZED DESIGN,
RANDOMIZED BLOCK DESIGN, LATIN
SQUARE DESIGN , OTHER DESIGNS.
D. Kavitha
MSc(N); MSc(Psy);BSAM; DHHM Ph.D Scholar

2.
Experimental Research

3.
Research design
 It is master plan specifying the methods and
procedures for following for collecting and
analyzing the needed information in a research
study

4.
Experimental research design
…the researcher selects participants and divides
them into two or more groups having similar
characteristics and, then, applies the
treatment(s) to the groups and measures the
effects upon the groups

5.
Uniqueness of experimental
research design
• Experimental Research is unique in two
important respects:
1) Only type of research that attempts to influence a
particular variable
2) Best type of research for testing hypotheses about
cause-and-effect relationships
• Experimental Research looks at the following
variables:
• Independent variable (treatment)
• Dependent variable (outcome)

6.
Major Characteristics of
Experimental Research
• The researcher manipulates the independent variable.
• They decide the nature and the extent of the
treatment.
• After the treatment has been administered,
researchers observe or measure the groups receiving
the treatments to see if they differ.
• Experimental research enables researchers to go
beyond description and prediction, and attempt to
determine what caused effects.

7.
Essential Characteristics of
Experimental Research
Comparison of Groups:
• The experimental group receives a treatment of some sort while
the control group receives no treatment.
• Enables the researcher to determine whether the treatment has
had an effect or whether one treatment is more effective than
another.
Manipulation of the Independent Variable:
• The researcher deliberately and directly determines what forms the
independent variable will take and which group will get which form.

8.
Essential Characteristics of
Experimental Research
Randomization
• Random assignment is similar but not identical to random selection.
• Random assignment means that every individual who is
participating in the experiment has an equal chance of being
assigned to any of the experimental or control groups.
• Random selection means that every member of a population has an
equal chance of being selected to be a member of the sample.
• Three things occur with random assignments of subjects:
1) It takes place before the experiment begins
2) Process of assigning the groups takes place
3) Groups should be equivalent

9.
Simple Random Sample
 Every subset of a specified size n from the
population has an equal chance of being
selected

10.
Stratified Random Sample
 The population is divided into two or more
groups called strata, according to some
criterion, such as geographic location, grade
level, age, or income, and subsamples are
randomly selected from each strata.

11.
Cluster Sample
 The population is divided into subgroups
(clusters) like families. A simple random
sample is taken of the subgroups and then all
members of the cluster selected are surveyed.

12.
Systematic Sample
 Every kth member ( for example: every 10th
person) is selected from a list of all population
members.

13.
Types of Designs
 The basic structure of a research study . . .
particularly relevant to experimental research
 Types of experimental designs (Campbell & Stanley,
1963)
 Pre-experimental
 Quasi-experimental
 True experimental

14.
Pre-experimental
design
Quasi –
experimental
design
True experimental
design
•One shot case design
•One group pretest-
posttest design
•FEATURES
•Manipulation of
independent variables
•Limited control over
the extraneous
variables
•No randomization and
control group
•Non randomized block
design
•Time series design
•FEATURES
•Manipulation of
independent variable
•Absence of either
randomization/ control
group
•Post –test only control
design
•Pre –test– posttest
control group design
•Factorial design
•Randomized block
design
•Cross over design
•FEATURES
•Manipulation of
independent variable
•Presence of control
group
•Randomization

15.
Variable
 a concept (e.g., intelligence, height, aptitude) that
can assume any one of a range of values
 Independent variable - an activity of
characteristic believed to make a difference with
respect to some behavior
 Ex - experimental variable, active variable, cause,
treatment
 Dependent variable - the change or difference
occurring a result of the independent variable
 Ex- Assigned variable, effect, outcome, posttest

16.
Steps in conducting
experimental research
 Decide if an experiment addresses the
research problem
 Form hypotheses to test cause-effect
relationships
 Select an experimental treatment and
introduce it
 Identify study participants choose a type of
experimental design
 Conduct the experiment
 Organize and analyze the data
 Develop an experimental research report

17.
 The concept of validity…the experiment tests the
variable(s) that it purports to test
 Threats to validity…
 Internal: factors other than the independent
variable that affect the dependent variable(
campbell 1963)
 External: factors that affect the generalizability of
the study to groups and settings beyond those of the
experiment

18.
Threats of internal validity
 History
 Maturation of subjects
 Testing
 Instrumentation change
 Mortality
 Selection bias – maturation interaction

19.
History
 Some event beside the experimental treatment
occurs during the course of the study , and this
event even influence dependent variable.

20.
Maturation of subjects
 Experimental research is carried on long
period of time over a group of subjects there
may be changes in the subjects in different
ways.
 Increase in height, weight.
 Ex. Nutritional protocol on height & weight of
malnourished children

21.
Testing
 Effect of taking a pretest of subjects’
performance of post test.
 The effect of taking a pretest may sensitize an
individual and improve the score of the post
test.
 Individuals generally score higher during
second test regardless of treatment.

22.
Instrument change
 Changes in instruments, calibration of
instruments, observers or scorers may cause
changes in the measurements

23.
Mortality
 Loss or dropout of the subject during course
of the study
 The longer period of study the more chance for
dropout.
 Ex. longitudinal study

24.
Selection bias
 Subjects are not selected randomly for
participation in groups , there is a possibility of
comparison may not equivalent.

25.
External validity
 Hawthorne effect
 Subjects may behave in particular manner
because they are aware that they are being
observed

26.
Experimental effect
 Threat to study results when researcher’s
characteristic , mannerism, behavior may
influence subject matter.

27.
Reactive effect of pretest
 Effect of pretest occurs when subjects have
been sensitized to the treatment because of
taking pretest.
 Ex – pretest may sensitize to learn about HIV/
AIDS irrespective of health education is
provided

28.
Novelty effect:
Treatment is new , the subjects and researchers act
different ways
People : Generalization is not applicable depending
upon the race.
Place: Generalization not possible for people living
in rural and urban area
Time : older results can not be generalized over
periods of time.

29.
Most common way to eliminate
threats
 Experimental control Experimental control attempts to
predict events that will occur in the experimental setting
by neutralizing the effects of other factors.
 Physical Control Gives all subjects equal exposure to
the independent variable. Controls non-experimental
variables that effect the dependent variable.
 Selective Control Indirectly manipulate by selecting in
or out variables that cannot be controlled
 Statistical Control Variables not conducive to physical
or selective manipulation may be controlled by statistical
techniques.

30.
Criteria for evaluating
experimental Research
 Does the experiment have a powerful
intervention?
 Does it employ few treatment groups (e.g. only
two)?
 Will participant profit from the intervention?
 Is there a systematic way the researcher
derived the number of participants per group?

31.
Criteria for evaluating
experimental Research
 Were there an adequate number of
participants used in the study?
 Were valid, reliable, and sensitive measures or
observations used?
 Did the study control for extraneous factors?
 Did the researcher control for threats to
internal validity?

32.
Types of pre experimental
design
 The One-Shot Case Study
 A single measure is recorded after the treatment
in administered.
 Study lacks any comparison or control of
extraneous influences.
 To remedy this design, a comparison could be
made with another group.
 Diagrammed as:

33.
The One-Group Pretest-Posttest Design
 Subjects are measured before and after treatment is
administered.
 Uncontrolled-for threats to internal validity exist.
 To remedy this design, a comparison group could be
added.
 Diagrammed as:

34.
The Static-Group Comparison
Design
 Use of 2 existing, or intact groups.
 Experimental group is measured after being
exposed to treatment.
 Control group is measured without having been
exposed to the treatment.
 Diagrammed as:

35.
The Static-Group Pretest-Posttest Design
 Pretest is given to both groups.
 “Gain” or “change” = pretest score -
posttest score.
 Better control of subject characteristics
threat.
 A pretest raises the possibility of a testing
threat.

36.
Pre experimental design
Advantages Disadvantages
Very simple
Convenient to conduct in
natural settings
Suitable for beginners
Weak design to establish
casual relationship between
independent and dependent
variable
Very little control over the
research
Higher threat to internal
validity

37.
Characteristic of quasi
experimental research design
 Manipulation of independent variable
 Lack of one / two essential character of true
experimental design
 Quasi independent variable used instead of
true independent variable.

38.
Types of quasi experimental
design
Nonequivalent /Non randomized control group
design
O X O
O O
random assignment of intact groups that are
pretested ( O ), exposed to a treatment ( X )
and then posttested ( O )
Time-series design
O O O O X O O O O
a single group is pretested ( O ) repeatedly until
pretest scores are stable, exposed to a
treatment ( X ) and, then, is repeatedly
posttested ( O )

39.
Possible Outcome Patterns in
a Time-Series Design

40.
Characteristics of true
experimental design
 Manipulation – control of independent
variable by the researcher through treatment/
intervention
 Control – the use of control group and
extraneous variables on the dependent
variable
 Randomization – every subject gets equal
chance being assigned to experimental and
control group.

41.
Advantages Disadvantage
s
Most powerful design to establish
causal relationship between
independent and dependent
variable
Cannot be replicated in studies
conducted in human begins due
ethical problems
Purity of the observation Many of the human variables
neither have valid measurable
criteria nor instruments to
measure.
Create conditions in a short period
of time that may take years to
occur naturally
Studies conducted in hospital /
community difficult to control the
extraneous variable
Conducted in laboratory,
experimental unit, specialized
research setting
Very difficult get co operation for
treatment/ intervention

42.
True Experimental
• The essential ingredient of a true experiment is
random assignment of subjects to treatment groups
• Random assignments is a powerful tool for
controlling threats to internal validity
– The Randomized Posttest-only Control Group Design
• Both groups receiving different treatments
– The Randomized Pretest-Posttest Control Group
Design
• Pretest is included in this design
– The Randomized Solomon Four-Group Design
• Four groups used, with two pre-tested and two not pre-tested

43.
The Randomized Posttest-Only
Control Group Design
 Experimental group tested after treatment exposure.
 Control group tested at the same time without exposure
to experimental treatment.
 Includes random assignment to groups.
 Threats to internal validity – mortality, attitudinal,
implementation, data collector bias, location and history.

44.
Example of a Randomized Posttest-
Only Control Group Design

45.
The Randomized Pretest-
Posttest Control Group Design
 Experimental group tested before and
after treatment exposure
 Control group tested at same two times
without exposure to experimental
treatment
 Includes random assignment to groups.
 Pretest raises the possibility of a pretest
treatment interaction threat

46.
Example of a Randomized Pretest-
Posttest Control Group Design

47.
The Randomized Solomon Four-
Group Design
 Combines pretest-posttest with control group
design and the posttest-only with control
group design.
 Provides means of controlling the interactive
test effect and other sources of extraneous
variation.
 Does include random assignment.
 Weakness: requires a large sample.

48.
Example of a Randomized Solomon
Four-Group Design

49.
A Randomized Posttest-Only Control
Group Design

50.
Solomon four-group design
R O X1 O
R O X2 O
R X1 O
R X2 O
four groups are formed by random assignment
( R ) of participants, two groups are pretested
( O ) and two are not, one pretested and one
un pretested group receive the experimental
treatments ( X1, X2 ), each group is are
administered a posttest on the dependent
variable, and posttest scores are compared to
determine effectiveness of treatments

51.
Factorial design
 involve two or more independent variables
with at least one independent variable being
manipulated by the researcher
two-by-two factorial design (four cells)
2 X 2
 two types of factors (e.g., method of
instruction) each of which has two levels (e.g.,
traditional vs. innovative)

52.
Using a Factorial Design to Study
Effects of Method and Class Size on
Achievement

53.
Illustration of Interaction and No
Interaction in a 2 by 2 Factorial
Design

54.
Example of a 4 by 2 Factorial
Design

55.
Randomized block design
 Principle of local control along with other two
principle of experimental design
 subjects are first divided into groups
 each group the subjects are relatively
homogeneous
 The number of the equal in each group
 Extraneous variable is fixed

56.
Type of
antihypert
ensive
drugs
Blocks
Patients with
primary
hypertension
DM patients
with
hypertension
Renal
patients with
hypertension
A A,I B,II A,III
B B,I B,II B,III
C C,I C,II C,III

57.
Cross over design / repeat
measure design
 Subjects exposed more than one treatment
 Subjects randomly assigned to different orders
of treatment
 Equal distribution of character among the
group

58.
Latin square design
 very frequently used in agricultural research.
 An experiment has to be made through which
the effects of five different varieties of
fertilizers on the yield of a certain crop.
 out put occur depend on soil not only on the
fertilizer
 L.S. design is used when there are two major
extraneous factors such as the varying soil
fertility and varying seeds

59.
Seed
Differen
ces
FERTILITY LEVEL
X1 A B C D E
X2 B C D E A
X3 C D E A B
X4 D E A B C
X5 E A B C D

60.
Other designs
Descriptive design
 Univariant descriptive design – the frequency
of occurrence of the phenomenon
 Ex – the experience of patients suffering from
rheumatoid arthritis
 Prevalence of vitamin D deficiency among
pregnant women
 Used to identify, describe the perception,
awareness, behavior, attitude, knowledge and
practice of people.

61.
Exploratory design
 Used to identify , explore and describe the
existing phenomenon and its related factors
 Ex . contributing factors of sleep disturbance
among patients admitted in ICU

62.
Comparative design
 Comparing and contrasting two or more
sample of subjects on one or more variable
 Attributes-Knowledge, perception, attitudes
 Physical and psychological symptoms
 Ex KAP on Vitamin D among antenatal
mothers

63.
Prospective Cohort Study
Some have the
factor (c)
Population
(lapse of time)
Begin enquiry here
& work forwards
Sample people
without
the disease
Disease (a)
Disease (b)
No Disease
No Disease
Statistic = Relative Risk [RR] = (a/c) divided by (b/d)
This shows the ratio of incidence in exposed
compared to non-exposed.
RR > 1 implies a hazard;
RR < 1 implies a protective factor
95% CI are usually presented:
e.g., RR = 1.9 (95% CI 1.5, 2.3)
Note: as you begin
with people who do not
have the disease, you
can calculate incidence
but not prevalence.
(Prevalence would be
underestimated as you
omitted existing
cases)
Some do not (d)
Outcomes

64.
Retrospective Case-Control Study
Population
Select
Cases
(have the
disease)
Sample of
Controls
(who do not
have the
disease)
Exposed (c)
Exposed (a)
Not Exposed (d)
Not Exposed (b)
Begin enquiry here
& look backwards
Statistic = Odds Ratio [OR] = (a/b) divided by (c/d)
This shows how many times more likely were the cases
to have been exposed than the controls.
OR interpreted in same way as RR
Review
history
Review
history
Note: as you begin
with people who already
have the disease, you
cannot calculate
incidence or prevalence

65.
Developmental research
design
Cross sectional design
 Researcher collect data at particular point of
time
 Ex –assessing the awareness on swine flu
among people of an area
Longitudinal design
 Collect the extended period of time
 follow up studies

66.
Other type of trails
 Pilot studies and feasibility studies– run before
a large trail take place
 Screening trails – cervical cancer screening
trail
 Prevention trails – breast cancer prevention
trail.
 Trails looking at causes and patterns of
disease
 Case control studies
 Sequential trails

67.
Conclusion
 There are several research designs and the
researcher must decide in advance of
collection and analysis of data as to which
design would prove to be more appropriate for
his research project.

68.
Applying What you Have
Learned: An Experimental Study
Review the article and look for the following:
 The research problem and use of quantitative
research
 Use of the literature
 The purpose statement and research
hypothesis
 Types and procedures of data collection
 Types and procedures of data analysis and
interpretation
 The overall report structure