EXPERIMENTAL DESIGNS COMPLETELY RANDOMIZED DESIGN, RANDOMIZED BLOCK DESIGN, LATIN SQUARE DESIGN , OTHER DESIGNS.
D. Kavitha
MSc(N); MSc(Psy);BSAM; DHHM Ph.D Scholar
Experimental Research
Research design
It is master plan specifying the methods and procedures for following for collecting and analyzing the needed information in a research study
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
Uniqueness of experimental research design
• Experimental Research is unique in two important respects:1) Only type of research that attempts to
influence a particular variable2) 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)
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.
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.
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 begins2) Process of assigning the groups takes place3) Groups should be equivalent
Simple Random Sample
Every subset of a specified size n from the population has an equal chance of being selected
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.
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.
Systematic Sample
Every kth member ( for example: every 10th person) is selected from a list of all population members.
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
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
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
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
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
Threats of internal validity
History Maturation of subjects Testing Instrumentation change Mortality Selection bias – maturation interaction
History
Some event beside the experimental treatment occurs during the course of the study , and this event even influence dependent variable.
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
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.
Instrument change
Changes in instruments, calibration of instruments, observers or scorers may cause changes in the measurements
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
Selection bias
Subjects are not selected randomly for participation in groups , there is a possibility of comparison may not equivalent.
External validity
Hawthorne effect Subjects may behave in particular
manner because they are aware that they are being observed
Experimental effect
Threat to study results when researcher’s characteristic , mannerism, behavior may influence subject matter.
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
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.
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.
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?
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?
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:
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:
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:
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.
Pre experimental design
Advantages DisadvantagesVery simpleConvenient 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
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.
Types of quasi experimental design
Nonequivalent /Non randomized control group design
O X O O Orandom 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 )
Possible Outcome Patterns in a Time-
Series Design
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.
Advantages Disadvantages
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
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
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.
Example of a Randomized Posttest-Only Control Group
Design
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
Example of a Randomized Pretest-Posttest Control Group
Design
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.
Example of a Randomized Solomon
Four-Group Design
A Randomized Posttest-Only Control Group Design
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
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)
Using a Factorial Design to Study Effects of Method and Class Size
on Achievement
Illustration of Interaction and No Interaction in a 2 by 2 Factorial Design
Example of a 4 by 2 Factorial Design
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
Type of antihypertensive 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
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
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
SeedDifferences
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
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.
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
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
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 beginwith people who do nothave the disease, youcan calculate incidencebut not prevalence.(Prevalence would beunderestimated as youomitted existing cases)
Some do not (d)
Outcomes
Retrospective Case-Control Study
Population
SelectCases
(have the disease)
Sample ofControls
(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
Reviewhistory
Reviewhistory
Note: as you beginwith people who alreadyhave the disease, youcannot calculateincidence or prevalence
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 areaLongitudinal design Collect the extended period of time follow up studies
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
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.
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
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