Experimental research design

EXPERIMENTAL
RESEARCH
DESIGN
MR. JAYESH PATIDAR
www.drjayeshpatidar.blogspot.com

INTRODUCTION…
 Experimental is most scientifically
sophisticated research method.
 It is defined as ‘observation under controlled
conditions’.
 Experimental research design are concerned
with examination of the effect of independent
variable on the dependent variable, where the
independent variable is manipulated through
treatment or intervention(s), & the effect of
those interventions is observed on the
dependant variable.

TRUE
EXPERIMENTAL
DESIGN

CONCEPT…
True experimental research designs
are those where researchers have
complete control over the extraneous
variables & can predict confidently
that the observed effect on the
dependable variable is only due to the
manipulation of the independent
variable.

ESSENTIAL CHARACTERISTICS…
 A true experimental research design must essentially
consist of the following three characteristics:
 Manipulation
 Control
 Randomization

MANIPULATION:
 Manipulation refers to conscious control of
the independent variable by the
researcher through treatment or
intervention(s) to observe its effect on the
dependent variable.
 In other words, it is a conscious act by the
researcher, where he or she varies the
independent variable & observes the
effect that manipulation has on the
dependant variable of interest.

COUNT…
 For example, a researcher is conducting a
study on efficacy of cholrhexidine mouthwash
on the prevention of ventilator-associated
pneumonia (VAP) among patients admitted in
ICUs.
 In this example, chlorhexidine mouthwash is
the dependent variable, which is manipulated
by the researcher, & is used as an
intervention for the experimental group, while
the control group is kept deprived of it to
observe its effect on the incidence of VAP.

CONTROL:
 Control is another essential element of true
experimental design.
 Control refers to use of control group &
controlling the effects of extraneous
variables on the dependent variable in
which researcher is interested.
 The subject in the control & experimental
groups are similar in number &
characteristics, but the subject in the control
group receive no experimental treatment or
any intervention at all.

COUNT…
 The experimental group receives the planned
treatment or intervention & a comparison is
made with the control group to observe the
effect of this treatment or intervention.
 Generally in health care & nursing research, it
is not ethically feasible keep a control group
deprived of interventions; however, existing
conventional method of interventions may be
compared with experimental interventions.

RANDOMIZATION:
 Randomization means that every subject has an equal
chance of being assigned to experimental or of study
subjects on a random basis.
 Through random assignment of subject under
experimental or control group, chances of systemic bias
is eliminated.
 Randomization is used in true experimental research
design to minimize the threat of internal validity of the
study & to eliminate the effect of extraneous variables on
dependent variables.
 Through randomization, on average the characteristics of
the subject in experimental & control groups are similar,
thus influence of extraneous variables on dependant
variable is eliminated by dispersing the variability of the
subject characteristics equally in both the groups.

COUNT…
METHODS OF RANDOMIZATION:
 Random assignment of subject may done with simple flip
of a coin for each subject; if coin lands on its ‘head’,
subjects are assigned to first group & with ‘tail’ subjects
are assigned to control group.
 Another possible method is to write the names of the
subjects on slips of paper & put the slips into a bowl &
then draw lots. The first designated numbers of subjects
are placed in one group, & rest are assigned under
another group.
 Thirdly a random table may be used to facilitate the
randomization process. In this method, blind-folded
subjects choose a number from a table of number
horizontally (row) or vertically (columns), till a requisite
number is reached for both experimental & control
groups. Computer-assisted random sequences also may
be used for the random assignment of the subjects

TYPES OF THRUE EXPERIEMNTAL DESIGN
True Experiential Design
Post-test
only
Factorial
Pretest
post-test
only
Crossover
Solomon 4
groups
Randomized
block

POST-TEST-ONLY CONTROL DESIGN:
 Composed of two randomly assigned group, i.e.
experimental & control, but neither of which is pretested
before the implementation of treatment on the
experimental group.
 In addition, while treatment is implement on the
experimental group only, post-test observation is carried
out on both the group to assess the effect of
manipulation.
 This design can be helpful in situations where it is not
possible to pretest the subjects.
 For example, to study the effect of an educational
intervention related to urinary incontinence on the
subsequent help-seeking behavior of older adults.

COUNT…
Random
assignment
Exp. group Treatment Post-test
Control group Post-test

PRETEST-POST-TEST-ONLY DESIGN
 In this research designs, subjects are randomly assigned
to either the experimental pr the control group.
 The effect of the dependent variable on both the groups
is seen before the treatment (pretest).
 Later, the treatment is carried out on experimental group
only, & after-treatment observation of dependant variable
is made on both the groups to examine the effect of the
manipulation of independent variable on dependant
variable.
 For example, such a design could be used for ‘an
experimental study to assess the effectiveness of
cognitive behavioral therapy interventions for patients
with breast cancer.’

COUNT…
Random
assignment
Exp.
group
Treatment
Post-
test
Control
group
Post-test
pretest
pretest

SOLOMON FOUR-GROUP DESIGN
 There are two experimental groups (experimental group
1 & experimental group 2) & two control groups (control
group 1 & control group 2).
 Initially, the investigator randomly assigns subjects to the
four groups.
 Out of the four groups, only experimental group 1 &
control group1 receives the pretest, followed by the
treatment to the experimental group 1 & experimental
group 2.
 Finally, all the four groups receive post-test, where the
effects of the dependant variables of the study are
observed & comparison is made of the four groups to
assess the effect of independent variable (experimental
treatment) on the dependant variable.

COUNT…
 In this, experimental group 2 was observed at
one occasion, & that score should be similar to
average scores of those in experimental &
control groups.
 To estimate the amount of change in
experimental & control group 2, the average
test scores of experimental & control groups 1
are used as baseline
 The solomon four-group design is believed to
be most prestigious experimental research
design, because it minimizes the threat to
internal & external validity.

COUNT…
Random
assignment
Exp. Group 1
Control Group 1
Exp. Group 2
Control Group 2
pretest treatment Post-test
pretest Post-test
treatment Post-test
Post-test

FACTORIAL DESIGN
 In factorial design, researcher manipulates two or more
independent variables simultaneously to observe their effects on
the dependant variables.
 This design is useful when there are more than two independent
variables, called factors to be tested.
 For example, a researcher wants to observe the effect of two
different protocols of mouth care on prevention of VAP when
performed at different frequencies in a day.
 This design also facilitates the testing of several hypothesis at a
single time.
 Typical factorial design incorporates 2X2 or 2X3 factorial, but it
can be in any combination.
 The first number (α) refers to the independent variables or the
type of experimental treatments, & the second number (β) refers
to the level or frequency of the treatment.

COUNT…
Frequency
of mouth
care
Protocols of the mouth care
Chlorhexidine
(α1)
Saline (α2)
4 hourly (β1) α1….β1 α2….β1

RANDOMIZED BLOCK DESIGN
 Control of inherent differences between
experimental subjects & differences in
experimental conditions is one of the difficult
problems faced by researcher in biological
sciences.
 When there are a large number of experimental
comparison groups, the randomized block
design is used to bring homogeneity among
selected different groups.
 This is simple method to reduce the variability
among the treatment groups by a more
homogeneous combination of the subjects
through randomized block design.

COUNT…
 For example, a researcher wants to examine
the effects of three different antihypertensive
drugs on patients with hypertension.
 In this example, to ensure the homogeneity
among the subjects under
treatment, researcher randomly places the
subjects in homogeneous groups (blocks) like
patients with primary hypertension, diabetic
patients with hypertension, & renal patients
with hypertension .

COUNT…
Types of
antihypertensive
drugs
Blocks
Patients with
primary
hypertension (I)
Diabetic patients
with hyper
tension (II)
Renal patients
with
hypertension
(III)
A A, I A, II A, III
B B, I B, II B, III
C C, I C, II C, III

CROSSOVER DESIGN
 In this design, subjects are exposed to more than one
treatment, where subjects are randomly assigned to
different orders of treatment.
 It is also known as ‘repeat measures design’.
 This design is more efficient in establishing the highest
possible similarity among subjects exposed to different
conditions, where groups compared obviously have
equal distribution of characteristics.
 Through crossover design is considered as an extremely
powerful research design, sometimes it is not effective
because when subjects are exposed to two different
conditions, their responses of the second condition may
be influenced by their experience in the first condition.

COUNT…
 For example, when we are comparing the
effectiveness of the chlorhexidine mouth care protocol
on group I & saline mouth care protocol on the subjects
of group II.
 Later, the treatment is swapped, where group I
receives the saline mouth care & group II receives
chlorhexidine. In such studies, subjects serve as their
own control.
Groups Protocols of the mouth care
Group I Chlorhexidine (α1) Saline (α2)
Group II Saline (α2) Chlorhexidine (α1)

ADVANTAGES OF TRUE EXPERIMENTAL
DESIGN
 Experimental research designs are considered the
most powerful designs to establish the causal
relationship between independent & dependant
variables.
 Where the purpose of research is explanation,
causal relationship may be established among the
variables by experimentation, especially in studies
involving physical objects, where the variables are
more easily controlled than in human studies.
 In this studies, the controlled environment in which
the study is conducted can yield a greater degree
of purity in observation.

COUNT…
 Conditions not found in a natural setting can be created in
an experimental setting, where the independent variable is
manipulated by investigator.
 In the experimental approach, we can often create
conditions in a short period of time that may take years to
occur naturally. For example, in genetic studies we can
breed strains in very small time, which would take a long
time in nature to occur.
 When the experiment is conducted in a laboratory,
experimental unit, or other specialized research setting, it
is removed from the pressure & problems of real-life
situations & the researcher can pursue his or her studies in
a more leisurely, careful, & concentrated way.

DISADVANTAGES OF TRUE EXPERIMENTAL DESIGN
 Most of the times, the results of experimental research
designs cannot be replicated in studies conducted on
human beings due to ethical problems.
 For certain research problems, because of the danger to
physical & psychological health of the human subjects, it
is not possible to conduct experiments on human beings.
 Many of the human variables neither have valid
measurable criteria nor instruments to measure them. For
example, patient welfare or level of wellness cannot be
measured on any scale or by any instrument. In these
situations, if a refined experimental design is used, there
may be a mismatch of research design & the variable-
measuring instruments.

COUNT…
 In experimental studies conducted in natural
settings like hospitals or community, it is not
possible to impose control over extraneous
variables.
 Another disadvantage of the experimental
research design is that it is very difficult to get
cooperation from the study participants,
because it may involve medical or surgical
treatment or intervention, which may make the
prospective subjects reluctant to participate in
research study.

QUASI –
EXPERIMENTAL
RESEARCH
DESIGN

INTRODUCTION…
 Quasi-experimental research design involves the
manipulation of independent variable to observe to effect
on dependant variable, but it lacks at least one of the two
characteristics of the true experimental design;
randomization or a control group.
 In other words, quasi-experimental designs have an
element of manipulation but lack at least one of the other
two properties that characterize true experiments;
randomization or a control group.
 Quasi-experimental designs are generally used to
establish the causality (effect of independent variable on
dependent variable) in situations where researchers are
not able to randomly assign the subjects to groups or for
various reasons no control group is available for an
experimental study.

MAIN CHARACTERISTICS…
 Manipulation of the independent variables to
observe the effects on the dependant variables.
 Lack of at least one of the two other essential
characteristics of the true experiment, i.e.
random assignment of subject or a control
group.
 Quasi-independent variables are used instead
of true independent variables. Where
independent variable is not manipulates in
complete controller situations.

TYPES OF QUASI-EXPERIMENTAL DESIGN
Nonrandomized control group design
Time-series design

NONRANDOMIZED CONTROL GROUP DESIGN
 It is also known as the ‘nonequivalent control group
design’.
 This design is identical to the pretest-posttest control
group design, except there is no random assignment of
subjects in experimental & control groups.
 In this design, experimental & control groups are selected
without randomization, & dependent variables are
observed in experimental as well as control groups
before the intervention.
 Later, the experimental group receives treatment & after
that posttest observation of dependant variables is
carried out for both the groups to assess the effect of
treatment on experiment group.

COUNT...
Exp. group
Control group
Pretest
Pretest
Treatment Post-test
Post-test

COUNT…
 For example, this method was used to study ‘the effects of
integrated care on quality of work in nursing homes: a quasi-
experiment’.
 The purpose of this study was to examine the implementation of
integrated care in the nursing home sector, & its effect on the quality
of work of the caregivers.
 A nonequivalent pretest-posttest control group design was used in
this study.
 Data was collected by through a questionnaire.
 The result showed that the intervention appeared to be one
successful on the somatic wards.
 The caregivers of these wards were more successful in creating a
home-like environment for their residents.
 Regarding the effects of the intervention on the quality of work
factors, the result included an increase of social support by
supervision.
 The intervention on the psychosomatic wards was unsuccessful,
through the introduction of integrated care on the somatic wards
was fairly successful.

TIME-SERIES DESIGN
 This design is useful when the experimenter wants to
measure the effects of a treatment over a long period of time.
 The experimenter would continue to administer the treatment
& measure the effects a number of times during the course of
the experiment.
 Generally it is a single-subject research, in which the
researcher carries out an experiment on an individual or on a
small number of individuals, by alternating between
administering & then withdrawing the treatment to determine
the effectiveness of the intervention.
Exp.
group O1 O3O2 O3O2O1Treatment

COUNT…
 A researcher might assess pain levels of a
group of patients with low-back pain. After 3
weeks of pain assessment, subjects are
taught special exercises to reduce that pain.
During the next 3 weeks, pain levels would
again be measured.
 Measuring a child’s school performance on
a weekly basis, & then introducing a new
teaching technique. Then again measuring
on a weekly basis.

ADVANTAGES OF QUASI-EXPERIMENTAL DESIGN
 Quasi-experimental designs are more frequently used
because they are more practical & feasible to conduct
research studies in nursing, where in the absence of a
large sample size, randomization &/ or availability of
control groups are not always possible.
 This design is more suitable for real-world natural setting
than true experimental research designs.
 It allows researchers to evaluate the impact of quasi-
independent variables under naturally occurring
conditions.
 It may be able to establishing casual relationship.
Wherein some of the hypotheses are practically answered
through this design only.

DISADVANTAGES OF QUASI-EXPERIMENTAL
DESIGN
 There is no control over extraneous
variables influencing the dependant
variables.
 The absence of a control group or lack of
control over the research setting makes the
results of this design less reliable & weak for
the establishment of casual relationship
between independent & dependant
variables.

PRE –
EXPERIMENTAL
RESEARCH
DESIGN

 This research design is considered very weak, because
the researcher has very little control over the experiment
TYPES OF PRE-EXPERIMENTAL RESEARCH DESIGN:
o One-shot case design
o One-group pretest-posttest design

ONE-SHOT CASE DESIGN
 In this research design, a single
experimental group is exposed to a
treatment & observations are made after the
implementation of that treatment.
 There is no random assignment of subjects
to the experimental group & no control
group at all.
Exp. group Treatment Post-test

ONE-GROUP PRETEST-POSTTEST DESIGN
 It is the simplest type of pre-experimental design, where
only the experimental group is selected as the study
subjects.
 A pretest observation of the dependant variables is
made before implementation of the treatment to the
selected group, the treatment is administered, & finally a
posttest observation of dependant variables is carried
out to assess the effect of treatment on the group.
 Some researcher also argue this design as sub type of
quasi-experimental research design. However in
absence of both randomization & control group.
 This design ethically can not be placed under the
classification of quasi-experimental research design.

COUNT…
Exp. group Pretest Treatment Post-test

ADVANTAGES OF PRE-EXPERIMENTAL DESIGN:
o Very simple & convenient to conduct these studies in natural
settings, especially in nursing.
o Most suitable design for the beginners in the field of
experimental research.
DISADVANTAGES OF PRE-EXPERIMENTAL DESIGN:
o Considered a very weak experimental design to establish
casual relationship between independent & dependant
variables, because it controls no threat to internal validity.
o It has very little control over the research.
o It has a higher threat to internal validity of research, & may
have a selection bias, which can be very serious threats for in
using this particular design.

Thank
You

Experimental research design

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