Research Design
Interactive Presentation
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the correct answer. A
Two Main Types of Research
Design
• Experimental Studies
– Studies that involve the control and
manipulation of variables
• Observational Studies (i.e., quasiexperimental studies)
– Studies that involve the observation of
individuals or the measurement of certain
outcomes. No attempt is made to affect the
outcome (e.g., no treatment is given).
Experimental and Observational
Studies
Both experimental and observational
studies aim to determine the cause(s) for
natural phenomena.
– Once the research question has been
defined, the next step is to determine which
type of research design will provide you with
the most accurate answer for the type of
question you are asking.
Experimental Studies
Experimental studies are conducted in
controlled conditions that allow the
researcher to minimize bias and obtain
valid, reliable results.
– All variable measurements and manipulations
are under researcher control. For this reason,
experimental studies are considered the “gold
standard” of research methodology.
Observational Studies
Observational studies are considered less
invasive than experimental studies because they
do not require a change of the environment.
– Observational studies are used when experimental
studies are not ethically possible (e.g., when studying
the association between a risk factor and a disease).
– Observational studies include many variables that are
not under researcher control and therefore are not
considered as effective in answering research
questions as experimental studies.
Difference Between Experimental
and Observational Studies:
Another key difference between
experimental and observational studies is
that experimental studies test for causal
relationships while observational studies
can only test for correlation.
Causal Relationship: A relationship in which
one variable can be said to be the cause of
another.
Correlation: The degree of relationship
between two different variables.
Correlation vs. Causation
• Note: Correlation does not mean causation. This
means that just because two variables are
related, it does not mean that one variable
causes the other.
– Example: There is a strong positive relationship, or
association, between men who use hair growth
products and men who have hair loss. This does not
mean that hair growth products cause hair loss.
• The only way to determine whether one variable
causes another variable is to conduct an
experimental study.
Purpose of Different Study
Designs
• Researchers design experimental studies whenever
possible. Many times ethical considerations require that
an observational study be performed instead of an
experimental study.
• For example, observational studies are the only option
where the variable being tested may be harmful.
– If a researcher wants to study the relationship between HPV and
cervical cancer, it would be unethical to administer the virus to
an experimental treatment group and compare their clinical
outcomes with a control group. Therefore, an observational
study would be necessary to study this relationship.
– Observational studies are often used in epidemiological studies,
psychological studies, and sociological studies.
Types of Observational Studies
• Cohort Studies (i.e., longitudinal studies)
– Prospective cohort studies
– Retrospective cohort studies
• Cross-Sectional Studies
Cohort Study
A research study that compares a
particular outcome (such as lung cancer)
in groups of individuals who are alike in
many ways but differ by the variable the
researcher is studying (e.g., female nurses
who smoke compared with those who do
not smoke)
Cohort Studies
Prospective Cohort Study: Outcomes
have not yet occurred as study begins
– Not always feasible as they take considerable time,
money, and resources to complete; and they require
a large number of subjects
Example: Track a group of people with and without a risk factor
through time to observe who develops the disease
Retrospective Cohort Study: Outcomes
have already occurred as the study begins
Example: Review old medical records of a group of people with
and without a risk factor and determine who developed the
disease from birth to death
Cross-Sectional Study
• A research study that involve multiple
observations (e.g., an interview or
questionnaire), which may be useful to
determine how variables affect each other at the
same time and period.
Example: Questionnaire to determine how income is
related to weight
• Cross-sectional studies can also provide a
snapshot of the frequency and characteristics of
a disease in a population at a particular point in
time.
Test For Understanding
• Go to the following website and read a
brief synopsis of an observational study
conducted by the Women’s Health
Initiative:
http://www.nhlbi.nih.gov/whi/os.htm
• What type of observational study was
conducted?
A
B
C
Prospective Cohort Study
Retrospective Cohort Study
Cross-Sectional Study
Very Good!
You are ready to move on to the next topic.
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A retrospective study follows a cohort back
in time. This study followed more than
93,000 postmenopausal women forward in
time for eight years.
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A cross-sectional study takes place at a
single point in time. This study followed
more than 93,000 postmenopausal women
for a period of eight years.
Experimental Studies
In PBS you investigated the effect of the
“fight or flight” response on heart rate. In
HBS you investigated the effect of different
factors of muscle fatigue. In MI you
learned how clinical trials are designed to
assess the safety and efficacy of
experimental treatments. All of these have
one thing in common – they are all
examples of experimental studies.
Experimental Studies
• Research studies conducted to determine the
effect that one variable has upon another
variable.
– Researcher maximizes control over as many aspects
of the environment as possible in order to prove
causation.
– Researcher designs studies that are reliable and
valid.
Reliable: A study in which another researcher can perform
exactly the same experiment and generate results with the
same statistical significance.
Valid: A study in which the results accurately describe the
real world.
Validity
Researchers design studies that minimize
or eliminate systematic errors, or biases,
in the data collection process.
• Valid studies allow scientists to generalize
conclusions from a given study to the real world.
• Biases can be minimized through the following:
– Control groups
– Randomization
– Blinding
Controlled and Randomized
Studies
• Controlled Study: One group receives the
treatment and another group does not.
• Randomized Study: The control group and
treatment group are chosen at random.
Blinding
• As you learned with clinical trials, blinding
(when performing studies involving
humans) allows researchers to eliminate
bias that participants or investigators have
introduced by having knowledge of the
treatment or control conditions in an
experiment.
• Single-blind
• Double-blind
• Triple-blind
Single-Blind
The participant does not know whether he
or she has been allocated to a treatment
or control group.
– Identifies the placebo effect, where
participants in the control group of an
experiment exhibit some of the effects of the
treatment because they think they are
receiving the treatment.
Double-Blind
Neither the participant nor the researcher
knows whether the participant has been
allocated to a treatment or control group.
– If a researcher knows that a participant is
going to receive a treatment, they may act
more cautiously than if they were
administering a control.
Triple-Blind
Neither the participant, the researcher, nor
the response gatherer knows whether the
participant has been allocated to a
treatment or control group.
– Prevents the response gatherer (i.e., the
person responsible for observing and
measuring data in an experiment) from being
influenced by membership knowledge of the
treatment and control groups.
Confounding Variables
• In order to ensure valid results, the
researcher must eliminate any
confounding variables that might affect
the results of the experiment.
Confounding Variable: A variable that was
not accounted for in the experimental design,
varies systematically with the dependent
variable, and prevents a clear interpretation of
the effect of the independent variable on the
dependent variable.
Example of a Confounding Variable
A soccer coach wanted to determine whether vitamins
would improve the team’s playing ability, so the coach
set up an experiment. The coach assigned the offensive
players into the experimental group and gave the players
vitamins. He assigned the defensive players into the
control group and gave them a placebo. The offensive
players also ran an extra two miles a day. At the end of
the two week study, the coach noted that the offensive
players were playing significantly better than the
defensive players.
– What are the confounding variables in this
experiment?
What should the coach have done
differently to ensure validity?
Because of the design of the experiment, there
is no way to determine whether the change in
performance is due to the vitamins, running two
extra miles a day, or the inherent difference
between the offensive and defensive players.
Both of these (running an extra two miles a day
and assignment of players to an experimental
group and control group) are confounding
variables.
– What should the coach have done differently to
ensure validity?
Test For Understanding
Answer Conclusion question 1 on Project
2.1.1 Scientific Research. Once you have
completed this question, you may proceed
to the next slide.
Test For Understanding
When the experimenter evaluates the
outcome of a study without knowing which
participants were in the experimental
versus control group and the participants
and data gatherers are also unaware of
group assignments, then the study is said
to be
A
B
C
Retrospective
Randomized
Triple-Blind
Very Good!
You are ready to move on to the next
question.
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A retrospective study follows a cohort back
in time. This is a controlled, experimental
study where all individuals involved did not
know who was assigned to the
experimental group and who was assigned
to the control group.
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A randomized study is an experimental
study where the participants are randomly
assigned to the control group or the
experimental group. Although this is a
controlled, experimental study, no mention
of how participants were assigned to
groups was mentioned.
Experimental vs. Observational
Study?
• Why would a researcher choose to
perform an experimental study instead of
an observational study?
Experimental Study
An experimental study would allow the
researcher to determine a causal
relationship between the independent
variable and the dependent variable. The
subject the researcher is studying must
allow the researcher to design a controlled
environment where all confounding
variables are eliminated.
Test For Understanding
A researcher wants to study the
relationship between diet and the
occurrence of breast cancer. Which type
of study should the researcher conduct?
A
B
C
Cohort Study
Cross-Sectional Study
Experimental Study
Very Good!
You have now completed the Research
Design Interactive Presentation.
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A cross-sectional study only involves a single
observation that is useful if an immediate
response to a specific question is required.
Because of the nature of determining the
relationship between diet and the occurrence of
breast cancer, following a cohort group
throughout a long period of time is the best
choice to determine correlation. Unfortunately,
this type of study will not allow the researcher to
determine whether the relationship between diet
and the occurrence of breast cancer is causal.
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An experimental study is only possible if the
researcher can control the environment.
Because of the nature of this study, there is no
way that the researcher can conduct an
experimental study. Following a cohort group
throughout a long period of time is the best
choice to determine correlation. Unfortunately,
this type of study will not allow the researcher to
determine whether the relationship between diet
and the occurrence of breast cancer is causal.