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Research Design
Interactive Presentation
Copyright 2021. Project Lead The Way, Inc.
PLTW Biomedical Science
Biomedical Innovation
2.1.1 Scientific Research

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Directions
To move forward, click this arrow at the bottom
right of the screen.
To go back, click this arrow at the bottom left of
the screen.
To answer a question, click the button with the
correct answer.
A B C D

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Two Main Types of Research
Design
• Experimental Studies
• Studies that involve the control and manipulation of
variables
• Observational Studies (i.e., quasi-experimental
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).

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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.

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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.

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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.

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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.

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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.

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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.

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Types of Observational Studies
• Cohort Studies (i.e., longitudinal studies)
• Prospective cohort studies
• Retrospective cohort studies
• Cross-Sectional Studies

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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)

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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

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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.

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Test For Understanding
• Go to the following website and read the abstract
of an observational study conducted by the
University of Oxford:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13913/pdf/b
cr-1-1-073.pdf
• What type of observational study was
conducted?
Prospective Cohort Study
Retrospective Cohort Study
Cross-Sectional Study
A
B
C

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Very Good!
You are ready to move on to the next topic.

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SORRY! Go Back and Try Again
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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SORRY! Go Back and Try Again
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.

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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.

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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.

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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

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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.

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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

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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.

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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.

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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.

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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.

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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?

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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?

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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.

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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
Retrospective
Randomized
Triple-Blind
B
C
A

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Very Good!
You are ready to move on to the next question.

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SORRY! Go Back and Try Again
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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SORRY! Go Back and Try Again
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.

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Experimental vs. Observational
Study?
• Why would a researcher choose to perform an
experimental study instead of an observational
study?

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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.

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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?
Cohort Study
Cross-Sectional Study
Experimental Study
C
B
A

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Very Good!
You have now completed the Research Design
Interactive Presentation.

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SORRY! Go Back and Try Again
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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SORRY! Go Back and Try Again
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.