Transcript EXPERIMENTAL RESEARCH DESIGN - myaccess

EXPERIMENTAL
RESEARCH
DESIGN
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.
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True
experimental
design
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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.
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ESSENTIAL CHARACTERISTICS…
 A true experimental research design must
essentially consist of the following three
characteristics:
 Manipulation
 Control
 Randomization
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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.
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 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.
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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.
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 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.
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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 7/18/2015
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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, blindfolded 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
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TYPES OF THRUE EXPERIEMNTAL
DESIGN
True Experiential Design
Crossover
Post-test
only
Randomized
block
Pretest
post-test
only
Solomon 4
groups
Factorial
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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.
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Exp. group
Treatment
Post-test
Random
assignment
Control group
Post-test
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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 7/18/2015
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Exp.
group
pretest
Treatment
Posttest
Random
assignment
Control
group
pretest
Post-test
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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
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 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.
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Exp. Group 1
Control Group 1
pretest
treatment
Post-test
Post-test
pretest
Random
assignment
Exp. Group 2
Control Group 2
treatment
Post-test
Post-test
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Factorial design
 In factorial design, researcher manipulates two or more
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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 7/18/2015
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Frequency Protocols of the mouth care
of mouth
Chlorhexidine
Saline (α2)
care
(α1)
4 hourly (β1)
α1….β1
α2….β1
6 hourly
α1….β2
α2….β2
(β2)
8 hourly
α1….β3
α2….β3
(β3)
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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
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through randomized block design.
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 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 .
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Types of
antihypertensive
drugs
A
B
C
Blocks
Patients with
primary
hypertension
(I)
Diabetic
patients with
hyper tension
(II)
Renal patients
with
hypertension
(III)
A, I
B, I
C, I
A, II
B, II
C, II
A, III
B, III
C, III
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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 the7/18/2015
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 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)
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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.
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 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.
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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
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instrument. In these situations, if a refined
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 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.
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Quasi –
experimental
research
design
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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
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researchers are not able to randomly assign the
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.
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Types of quasi-experimental design
 Nonrandomized control group design
 Time-series design
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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
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Exp. group
Pretest
Control group
Pretest
Treatment
Post-test
Post-test
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 For example, this method was used to study ‘the effects of
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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
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unsuccessful, through the introduction of integrated care
on
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.
O2
O3
group
O1
O2
O3
Treatment
O1
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 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.
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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.
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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.
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Pre –
experimental
research
design
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 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
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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
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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.
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Exp. group
Pretest
Treatment
Post-test
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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.
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