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Experimental Research
Cause + Effect Manipulation Control
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Cause + Effect
Cause(s) = Independent Variable(s) Effect(s) = Dependent Variable(s)
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True Experimental Research Designs
Difficult to use in nursing Nonexperimental designs more common
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Internal Validity
Are changes in the dependant variable due to effects of the independent variable alone?
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External Validity
To what degree can the results of the study be generalized to other people and other settings?
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Extraneous Variables
Variables that cannot be controlled May threaten internal and external validity
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Extraneous Variables
Confounding Intervening Study Limitations
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Extraneous Variables
Threaten internal and external validity Control of one creates problems with others
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Six Threats to Internal Validity
Selection Bias History Maturation Testing Instrumentation Change Mortality
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Selection Bias
Changes in the dependent variable due to subject differences and not the experimental treatment
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History
An event other than the experimental treatment occurs during the course of a study and influences the dependent variable
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Maturation
Changes that occur within subjects during an experimental study may influence the study results
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Testing
The influence of the pretest or knowledge of baseline data effects the posttest score
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Instrument Change
Instrument inaccuracy or judging influences the pretest or posttest scores
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Mortality
Attrition or drop out
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Major Threats to External Validity
Hawthorne effect Experimenter effect Reactive effects of the pretest
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Hawthorne Effect
Study participants respond in a certain manner, not because of the experimental treatment but because they are aware that they are being observed
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Double-blind Experiment
Prevents the Hawthorne effect Treatment assignments unknown to
researcher and subjects
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Experimenter Effect
Occurs in experimental research Researcher characteristics or behaviors
influence subject behaviors
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Examples of Influential Researcher Characteristics
Facial expressions Clothing Age Gender Type of jewelry Body build
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Rosenthal Effect
Occurs in nonexperimental research Interviewer characteristics or behaviors
influence respondent’s answers
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Reactive Effects of the Pretest (Measurement Effect)
Subjects are sensitized to the experimental treatment through taking the pretest
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Symbolic Presentation of Research Designs
Developed by Campbell and Stanley (1963) Used to depict research designs in a
symbolic form R = random assignment of subjects to a
group O = observation or measurement of
dependent variable X = experimental treatment or intervention
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Experimental Research Designs
True experimental Quasi-experimental Pre-experimental
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True Experimental Design
Internal validity are minimized Causality Researcher has a great deal of
control
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True Experimental Design Criteria
Researcher manipulates the experimental variable (s)
One experimental group and one comparison group
Subjects randomly assigned to groups
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Manipulation—First Criteria
The independent, or experimental, variable is controlled by the researcher
Researcher has control overo the type of experimental treatment that is
administered ando who will receive the treatment
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Comparison or Control Group—Second Criteria
Group that does not receive the experimental treatment
Receive usual treatment or no treatment
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Random Assignment—Third Criteria
Each subject has equal chance Decreases Selection Bias
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Experimental Designs
Pretest-posttest control group design Posttest-only design Solomon four-group design
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The Pretest-Posttest Control Group Design
Subjects randomly assigned to groups Pretest is given to both groups Experimental group receives experimental
treatment Comparison group receives routine treatment
or no treatment Posttest is given to both groups
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The Pretest-Posttest Control Group Design
R O1 X O2
R O1 O2
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The Pretest-Posttest Control Group Design
Advantage Controls for all Internal Validity Threats
Disadvantage Causes external threats and Possible reactive effects of the pretest
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The Posttest-Only Control Group Design
Subjects randomly assigned to groups Experimental group receives the
experimental treatment Comparison group receives routine treatment
or no treatment Posttest given to both groups Eliminates reactive effects of pretest
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The Posttest-Only Control Group Design
R X O1 (Experimental group)
R O1 (Comparison group)
Eliminates the reactive effects of the pretest on the posttest
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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)
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Solomon Four-Group Design
Advantages Minimizes threats to both internal and external
validity Differences between groups can be associated
with the experimental treatment Disadvantages
Requires large sample Statistical analysis is complicated
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Quasi-Experimental Designs
No comparison group No randomization Nonequivalent Control Group Design Time-series Design
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Quasi-Experimental Designs
Advantages Convenient Approximates the real world
Disadvantages Decreases researcher control Decreases researcher manipulation
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The Nonequivalent Control Group Design
Similar to pretest-posttest control group design
No random assignment of subjects to groups
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The Nonequivalent Control Group Design
O1 X O2 (Experimental Group)
O1 O2 (Comparison Group)
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The Nonequivalent Control Group Design
Biggest threat to internal validity Selection bias
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Time-Series Design
Researcher observes or measures the subjects
Experimental treatment administered between two of the observations
O1 O2 O3 X O4 O5 O6
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Time-Series Design
Threats to Internal Validity History Testing
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Learning Objective 8
Discuss two pre-experimental designs
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Pre-Experimental Designs
One-shot Case Study One-group Pretest-Posttest Design
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The One-Shot Case Study
X O Controls for no threats to Internal Validity Weak design
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The One-Group Preset-Posttest Design
O1 X O2
Threats to Internal Validity History Maturation Instrumentation Change
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Learning Objective 9
Discuss four types of nonexperimental designs
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Nonexperimental Research
Descriptive No manipulation No control of variables
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Nonexperimental Research
Survey Research Correlational Research Comparative Research Methodological Research
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Survey Research
Self-report data Phone, mail, or through personal contact
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Survey Research
Data collection methods Questionnaires Interviews
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Strengths of Survey Research
Provide accurate information on populations Use relatively small samples Collect large amounts of data quickly Minimal cost
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Weaknesses of Survey Research
Self-report data may be unreliable Subjects tend to provide socially acceptable
responses
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Correlational Research
Explores the relationship between two or more variables
One variable is X. The other variable is Y
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Correlational Coefficient
Indicates the strength and direction of relationships
Indicates positive (+) or negative (-) information
Perfect positive correlation: +1.00 Perfect negative correlation: -1.00 No correlation/relationship: 0.00 Reported through Pearson’s product-moment
correlation (Pearson r)
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Correlational Research
No manipulation of a variable Possible to identify an independent and
dependent variables
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Correlational Research
The independent variable Usually comes first in chronological order Influences the dependent variable
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Correlational Research
Purpose is to explain relationships between variables
Cannot establish cause and effect Useful for generating hypotheses Guides future experimental and quasi-
experimental studies
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Comparative Research
Examines differences between groups on dependent variable
No manipulation of the independent variable Independent variable is often a characteristic
of the subjects Independent variable cannot ethically be
manipulated
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Comparative Studies
Retrospective Ex post facto
Prospective
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Retrospective Comparative Study
Dependent variable (effect) is identified in the present
Researcher tries to determine the independent variable (cause) that preceded it
Cannot use an experimental approach for the study
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Prospective Studies
Independent variable (presumed cause) is identified in the present
Subjects are followed into the future in order to observe the possible occurrence of the dependent variable (effect)
May use an experimental approach
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Methodological Studies
Research Instruments and Methods Development Testing Evaluation
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Secondary Analysis Studies
Analyses data gathered in a previous study May test new hypotheses May ask new questions of the data Cost-effective Efficient
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Learning Objective 10
Describe two types of settings in which research is conducted
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Research Settings
Laboratory Studies Field Studies
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Laboratory Studies
Conducted in specially created environments Research environment controlled by
researcher
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Simulation Studies
Laboratory studies Subjects’ responses to descriptions of case
studies measured Real-life situations represented in studies
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Field Studies
Real-life setting “In the field” Very little control maintained by the
researcher Phenomena studied in the natural
environment Very appropriate for nursing research
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Learning Objective 11
Critique the design section of quantitative studies
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Critique of Quantitative Research Designs
Read the entire research report carefully Determine if the appropriate design is used
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Questions for the Critique
Does it test the hypothesis(es)? Does the design answer the research
question(s)? Is the researcher trying to determine cause-
and-effect? Is the researcher trying to describe a
phenomenon from the research subject’s point of view?
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Critiquing the Quantitative Research Design Is the design clearly identified in the research
report? Is the design appropriate to test the study
hypothesis(es) or answer the research question(s)? If the study used an experimental design, was the
most appropriate type of experimental design used?
If the study used an experimental design, what means were used to control for threats to internal validity? External validity?
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Critiquing the Quantitative Research Design
Does the research design allow the researcher to draw a cause-and-effect relationship between the variables?
If the design was nonexperimental, would an experimental design have been more appropriate?
What means were used to control for extraneous variables, such as subject characteristics, if a nonexperimental design was used?
