Experimental Studies in Epidemiology
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Experimental Studies
Nonexperimental
Studies
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Experimental study is concerned with
cause-
and
-effect
relationships
.
All experimental studies involve
manipulation
of the
independent
variable (
cause)
and
measurement
of the
dependent variable
(effect).
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The three broad categories of experimental study
designs are:
1.
True experimental,
2.
Quasi-experimental, and
3.
Pre-experime
ntal
.
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True experimental designs
are determined by three
criteria:
1.
Control
(the researcher manipulates the experimental
variable, at least one experimental and one
comparison
group
or
control group
are included in the study),
2.
Randomly
(to either the experimental or comparison
group).
3.
Manipulation
(independent variable is controlled by
the researcher).
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Three types of true experimental designs
are
:
1.
Pretest- posttest control group design
,
2.
Posttest-only control group design
, and
3.
Solomon four group design
.
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the
pretest- posttest control group design
R O
1
X O
2
(Experimental group)
R O
1
O
2
(Comparison group)
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the
posttest-only control group design
R X O
1
(Experimental group)
R O
1
(Comparison group)
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the
Solomon four group design
R O
1
X O
2
(Experimental group 1)
R O
1
O
2
(Comparison group 1)
R X O
2
(Experimental group 2)
R O
2
(Comparison group 2)
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Quasi-experimental designs
have either
no comparison
group
or
no random
assignment of
subjects to groups.
•
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Nonequivalent control group design
O
1
X O
2
(Experimental group)
O
1
O
2
(Comparison group)
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Two quasi-experimental designs
are:
1.
Nonequivalent control group
design and
2.
Time-series design.
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the time-series design.
O
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O
2
O
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X O
4
O
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O
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:
Pre-experimental designs are
those in which the researcher
has little control over the study.
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Two types of pre-experimental designs
are
:
One-shot case study
X O
One-group pretest-posttest
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X O
2
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.
Extraneous variables
, also called
study
limitations
,
confounding variables
, and
intervening variables
,
are
uncontrolled
variables
that may
influence study
results
.
these extraneous variables are called
threats to internal and external validity.
Internal validity
concerns the degree to which
changes
in the
dependent
variable (
effect
) can be
attributed to
the
independent
variable (
cause
).
External validity
concerns the degree to which
study
results
can be
generalized
to other people
and settings.
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Six threats to internal validity are :
1.
Selection bias,
2.
History,
3.
Maturation,
4.
Testing,
5.
Instrumentation change, and
6.
Mortality.
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Three threats to external validity
are
:
1.
Hawthorne effect,
2.
Experimenter effect, and
3.
Reactive effects of the pretest.
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There are many different types of
nonexperimental designs:
Survey studies
Correlational studies
Comparative studies (
retrospective
and Prospective studies)
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Methodological studies(
concerned with the
development, testing, and evaluation of research
instruments and methods).
Secondary analysis studies
Laboratory studies
Field studies
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Epidemiological studies and experimental studies play vital roles in understanding cause-and-effect relationships in research. Experimental studies involve manipulating independent variables and measuring dependent variables, with categories such as true experimental, quasi-experimental, and pre-experimental designs. True experimental designs are characterized by control, randomization, and manipulation criteria. Different types of true experimental designs include pretest-posttest control group, posttest-only control group, and Solomon four group designs.
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Presentation Transcript
Epidemiological studies Experimental Studies Nonexperimental Studies
Experimental study Experimental study is concerned with cause- and-effect relationships. All experimental studies involve manipulation of the independent variable (cause) and measurement of the dependent variable (effect).
Categories of experimental study The three broad categories of experimental study designs are: 1.True experimental, 2.Quasi-experimental, and 3. Pre-experimental.
True experimental designs True experimental designs are determined by three criteria: 1.Control (the researcher manipulates the experimental variable, at least one experimental and one comparison group or control group are included in the study), 2.Randomly (to either the experimental or comparison group). 3. Manipulation(independent variable is controlled by the researcher).
Types of True Experimental Designs Three types of true experimental designs are: 1.Pretest- posttest control group design, 2.Posttest-only control group design, and 3.Solomon four group design.
Types of True Experimental Designs the pretest- posttest control group design R O 1 X O2 (Experimental group) R O1 O2 (Comparison group)
Types of True Experimental Designs the posttest-only control group design R X O1 (Experimental group) R O1 (Comparison group)
Types of True Experimental Designs the Solomon four group design R O1 X O2 (Experimental group 1) R O1 O2 (Comparison group 1) R X O2 (Experimental group 2) R O2 (Comparison group 2)
Quasi-experimental designs Quasi-experimental designs have either no comparison groupor no random assignment of subjects to groups.
Quasi-experimental designs Nonequivalent control group design O1 X O2 (Experimental group) O1 O2 (Comparison group)
Types quasi-experimental designs Two quasi-experimental designs are: 1. Nonequivalent control group design and 2.Time-series design.
Types quasi-experimental designs the time-series design. O1 O2 O3 X O4 O5 O6
Pre-experimental designs: Pre-experimental designs are those in which the researcher has little control over the study.
Types of Pre experimental designs: Two types of pre-experimental designs are: One-shot case study X O One-group pretest-posttest O1 X O2
Extraneous variables that may influence study results in experimental studies. Extraneous variables, also called study limitations, confounding variables, and intervening variables, are uncontrolled variables that may influence study results.
these extraneous variables are called threats to internal and external validity. Internal validity concerns the degree to which changes in the dependent variable (effect) can be attributed to the independent variable (cause). External validity concerns the degree to which study results can be generalized to other people and settings.
Threats to internal validity Six threats to internal validity are : Selection bias, 2. History, 3. Maturation, 4. Testing, 5. Instrumentation change, and 6. Mortality. 1.
External Validity Three threats to external validity are : 1.Hawthorne effect, 2.Experimenter effect, and 3.Reactive effects of the pretest.
Nonexperimental Designs There are many different types of nonexperimental designs: Survey studies Correlational studies Comparative studies (retrospective and Prospective studies)
Types of Nonexperimental Designs Methodological studies(concerned with the development, testing, and evaluation of research instruments and methods). Secondary analysis studies Laboratory studies Field studies
