important point about different type of experimental research design.

1. ADDIS ABABA UNIVERSITY COLLEGE OF VETERINARY MEDICINE AND
AGRICULTURE
GROUPASSGNIMENT ON RESEARCH METHODS
Title: Experimental research and design
Group members
 Akinaw Wagari
 Berihun Dires
 Desta Sisay
 Eyob Gelan
 Fantahun Dereje
 Melese Yilma
 Roba Jilo
 Tigist Getachew
Submitted to: Reta Duguma (DVM, MVSc, Assistant Professor)
Nov 10, 2014
Bishoftu, Ethiopia

2. OUTLINES
Introduction
Objectives
Terms to be remembered
Unique features of experiments
A checklist for planning experiments
Kinds of experimental research design
Points to be remembered by researchers to choose one of the experimental
research designs
Experimental invalidity
Conclusion

3. 1. INTRODUCTION
• Statistical studies can be classified as being either observational or experimental. In an observational
study, no attempt is made to control the factors. In an experimental study, one or more factors are
controlled so that data can be obtained about how the factors influence the variables of interest.
Cause-and-effect relationships are easier to establish in experimental studies than in observational
studies.
• Observations can be collected from observational studies as well as from experiments, but only an
experiment allows conclusions to be drawn about cause and effect.
• The art of designing an experiment and the art of analysing an experiment are closely intertwined
and need to be studied side by side.

4. Cont…
In designing an experiment, one must take into account the analysis that will be performed.
In turn, the efficiency of the analysis will depend upon the particular experimental design
that is used to collect the data. Without these considerations, it is possible to invest much
time, effort and expense in the collection of data which seem relevant to the purpose at-hand
but which, in fact, contribute little to the research questions being asked.
 A guiding principle of experimental design is to “keep it simple.” Interpretation and
presentation of the results of experiments are generally clearer for simpler experiments.

5. Cont…
• There are three basic techniques fundamental to experimental design; which are replication,
blocking and randomization.
Replication: helps us to know about the variation in order to generalize any conclusion about
an experimental units so that it is relevant to all similar subjects.
 Blocking: to block an experiment is to divide or partition, the observations into groups called
blocks in such a way that the observations in each block are collected under relatively similar
experimental conditions.
Randomization: the purpose of randomization is to prevent systematic and personal biases
(experimenter bias) from being introduced into the experiment by the experimenter.
The first two help to increase precision in the experiment; the last is used to decrease bias.

6. 2. OBJECTIVES
• The purpose of an experiment can range from exploratory (discovering new important sources
of variability) to confirmatory (confirming that previously discovered sources of variability
are sufficiently major to warrant further study). Typically, an experiment may be run for one
or more of the following reasons:
To determine the principal causes of variation in a measured response,
To find the conditions that give rise to a maximum or minimum response,
To compare the responses achieved at different settings of controllable variables,
To obtain a mathematical model in order to predict future responses.

7. 3. TERMS TO BE DEFINED/REMEMBERED
• Experimental research also called empirical research or cause and effect method; it is a
data-based research, coming up with conclusions which are capable of being verified with
observation or experiment. To experiment means to actively change x and to observe the
response in ‘‘y”.
• Experimental research - an attempt by the researcher to maintain control over all factors that
may affect the result of an experiment. In doing this, the researcher attempts to determine or
predict what may occur.
• Experimental design - a blueprint of the procedure that enables the researcher to test his
hypothesis by reaching valid conclusions about relationships between independent and
dependent variables. It refers to the conceptual framework within which the experiment is
conducted.

8. Cont…
• A factor is a variable that the experimenter has selected for investigation.
• A treatment is a level of a factor.
• Experimental units are the objects of interest in the experiment.
• Internal validity asks did the experimental treatment make the difference in this specific
instance rather than other extraneous variables.
• External validity asks to what populations, settings, treatment variables and measurement
variables can this observe effect be generalized?

9. Cont…
• Experimental control refers to the researcher’s attempt to eliminate any differential
influence of extraneous variables. These includes:
Physical control: gives all subjects equal exposure to the independent variable. Controls non
experimental variables that affect the dependent variable.
Selective control - manipulate indirectly 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 (example: covariance).

10. 4. UNIQUE FEATURES OF EXPERIMENTS
• The investigator manipulates a variable directly (the independent variable).
• Empirical observations based on experiments provide the strongest argument for cause-effect
relationships.
• The research question (hypothesis) is often stated as the alternative hypothesis to the null
hypothesis, which is used to interpret differences in the empirical data.

11. Cont…
• Random sampling of subjects from population (insures sample is representative of
population).
• Random assignment of subjects to treatment and control (comparison) groups (insures
equivalency of groups; i.e., unknown variables that may influence outcome are equally
distributed across groups).
• Extraneous variables are controlled by 4 & 5 and other procedures if needed.
• After treatment, performance of subjects (dependent variable) in both groups is compared.

12. 5. A CHECKLIST FOR PLANNING EXPERIMENTS
• Define the objectives of the experiment
• Identify all sources of variation
• Choose a rule for assigning the
experimental units to the treatments
• Specify the measurements to be made, the
experimental procedure and the anticipated
difficulties
• Run a pilot experiment
• Specify the model
• Outline the analysis
• Calculate the number of observations that
need to be taken
• Review the above decisions. Revise, if
necessary.

13. 6. KINDS OF EXPERIMENTAL RESEARCH
There are two major types of design:
Informal experimental designs:
• Before-and-after without control design.
• After-only with control design.
• Before-and-after with control design
Formal experimental designs:
• Completely randomized design (C.R.
Design).
• Randomized block design (R.B.
Design).
• Latin square designs (L.S. Design).
• Factorial designs

14. 7. POINTS TO BE REMEMBERED BY RESEARCHERS TO CHOOSE ONE OF THE
EXPERIMENTAL RESEARCH DESIGNS
• Different types of experimental research can be conducted depending on the nature of subjects
and the instruments and the way data are collected and analysed.
 Will there be a control group?
 How many subjects will there be?
Will the subjects be randomly selected?
Will each group be pretested?
How will they obtained data to be analyzed?
What factors may affect the internal validity?
What factors may affect the external validity?

15. 8. EXPERIMENTAL INVALIDITY
• The hindrances to good research design are called sources of experimental invalidity. These
sources fall under two major subdivisions: internal invalidity and external invalidity.
 Internal invalidity asks the question, “Are the measurements I make on my dependent
(i.e., the variable I measure) variable influenced only by the treatment or are there other
influences which change it?”
 An experimental design suffers from internal invalidity when the other influences, called
extraneous sources of variation, have not been controlled by the researcher.
When extraneous variables have been controlled, researchers can be reasonably sure that
post-treatment measurements are influenced by the experimental treatment and not by
extraneous variables (history, maturation, testing, instrumentation, statistical regression,
differential selection, experimental mortality and selection-maturation interaction).

16. Cont…
External invalidity asks, “How confidently can I generalize my experimental findings to
the world?” Sources of external invalidity cause changes in the experimental groups so that
they no longer reflect the population from which they were drawn.
External invalidity hinders the ability to infer back. Sources of external invalidity: the reactive
effects of testing, the interaction of treatment and subject, the interaction of testing and
subject; and multiple treatment interference.

17. CONCLUSION
• Designing an experiment that produces reliable, valid and objective data is not easy. But
experimental research is the only direct way to measure cause and effect relationships among
variables.
• The data collection is usually the most costly and the most time consuming part of the
experimental procedure. Spending a little extra time in planning helps to ensure that the data
can be used to maximum advantage.
• No method of analysis can save a badly designed experiment.