hw 9
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School
University of Illinois, Urbana Champaign *
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Course
212
Subject
Medicine
Date
Apr 3, 2024
Type
Pages
12
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Results
Gigi Yik — 3rd Attempt
15
Out of 15 points
02:10
Time for this attempt
This assessment has unlimited attempts.
Your Answers:
1 / 1 point
Use this information to answer questions 1-4. Consider this fictional study, in which
researchers have been studying possible health effects related to vaping. Since a relatively
small percentage of the population vapes, the researchers recruited 1,551 who reported
vaping regularly and 1,612 people who had not previously vaped and had no interest in
Take Now
Attempt History
Results
Points
Score
(Highest score is kept)
Attempt 1
12 of 15
80%
Attempt 2
14 of 15
93.33%
Attempt 3
15 of 15
100%
(Highest score)
100%
1
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vaping. Over the next 12 months, the researchers asked participants to report any
ongoing sicknesses or medical conditions. One condition in particular was a diagnosis of
pneumonia. They noticed a difference in pneumonia rates for each group.
Size
Percent Reporting
Pneumonia
Vapers
1,551
3.93%
Non-vapers
1,612
5.86%
What kind of study is this?
Feedback
Based on answering correctly
Good job! The researchers first identified two cohorts (vapers and non-vapers) and then monitored them for various response outcomes (pneumonia vs. no pneumonia) over some period of time. Note that the researchers did not assign
the participants to vape or not vape, so this would simply be an observational study, rather than an experiment.
1 / 1 point
Which statement best explains what this study reveals?
An Experiment
A Cross-Sectional Study
A Cohort Study
A Case Control Study
Vaping is a likely preventative of pneumonia
There is an association between those who frequently vape and a decreased
risk for pneumonia, but it’s not clear whether vaping is causally related to
pneumonia
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Feedback
Based on answering correctly
Good choice. We notice that the rate of pneumonia is lower for the vaping group, but there could be a confounder here.
1 / 1 point
Which of the following describes a potential confounder
to the relationship described in
the previous question and be consistent with the data we found?
Feedback
Based on answering correctly
That’s right! This is the only factor that explains why vaping would be associated with lower risk of pneumonia in the form of a confounder.
The “Socializing” answer could describe a confounding relationship, but that explanation goes the opposite direction (the data said vapers are less
likely to get pneumonia, but this explanation only fits if they are more
likely). The “stronger lungs” factor would be mediating
variable that explains how vaping Vaping is a likely cause of increased risk for pneumonia
There is an association between those who frequently vape and increased
risk for
pneumonia, but it’s not clear whether vaping is causally related to pneumonia
Younger people are more likely to vape, and younger people might be
healthier and less likely to get pneumonia
Vaping may lead to stronger lungs, and that may help prevent onset of pneumonia
People who get pneumonia may have a less healthy diet
People who start vaping may have done that because they socialize more and get
respiratory viruses, making them more likely to get pneumonia than others
3
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begins a causal chain to lower pneumonia risk.
The “healthy diet” factor does not directly relate vaping habits, so it doesn’t explain a connection between the two.
1 / 1 point
The researchers are trying to decide if they should compare the risk of pneumonia by
calculating relative risk or an odds ratio. Does it matter which they use?
Feedback
Based on answering correctly
Nice! Relative risks are typically appropriate to calculate in all design situations except case-control designs (when natural incidence is not preserved in the sampling method). In those situations, we might use an odds ratios to estimate the risk comparison. In all other situations, we could validly construct either relative risk or an odds ratio, but relative risk is often preferred since it’s more straightforward to interpret.
1 / 1 point
An article in Medical Xpress reported a link between young people who take melatonin
and a decreased risk of self-harm. https://medicalxpress.com/news/2023-03-melatonin-
linked-decreased-self-harm-young.html
One explanation is that melatonin promotes better quality sleep, and better quality of
sleep results in better mental health and less inclination toward self harm. Does better
quality of sleep help explain this link? If so, what type of explanation is it?
Only a Relative Risk is appropriate to calculate for this particular design
Only an Odds Ratio is appropriate to calculate for this particular design
Both could be used, but Relative Risk is often preferred for being easier to
interpret
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Feedback
Based on answering correctly
Nice work! In this explanation, melatonin is believed to cause better sleep, and better sleep then leads to better mental health/less self harm tendencies. Melatonin may not be directly affecting mental health/self harm tendencies, but sleep helps mediate the connection.
1 / 1 point
Use this information for questions 6-7. A college study finds that students who use
Adderall tend to have lower GPAs on average than students who don’t. Further
investigation shows that people who struggle with executive functioning (like
concentration) are more likely to use Adderall, and it’s actually their difficulties with
executive functioning that hurt their grades, not the Adderall. The Adderall may actually
help them perform better than they would otherwise.
Does difficulty with executive functioning help explain this link? If so, what type of
explanation is it?
Feedback
Based on answering correctly
Yes, as a Confounder
Yes, as a Mediator
No, it does not explain the link
Yes, as a Confounder
Yes, as a Mediator
No, it does not explain the link
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Nice job! Adderall doesn’t begin the causal chain here. Rather, it’s difficulty with executive functioning that leads people to try Adderall, and it’s difficulty with executive functioning that probably hurts grades. Adderall and lower grades are both outcomes of this confounder.
1 / 1 point
Now consider this same example again. Further investigation shows that people who take
Adderall are also more likely to have pets. Does having pets help explain this link? If so, what type of explanation is it?
Feedback
Based on answering correctly
Good job! There is nothing in the description that explains why pets would relate to GPA. So this doesn’t explain why Adderall would be linked to lower grades.
1 / 1 point
Use this information for questions 8-9. A doctor is studying whether having a particular
gene variant might increase your risk of an astigmatism (the condition that makes people
far-sighted or near-sighted). The researcher collected this data using an observational
study format, where she compared people with the gene variant to people without the
gene variant to see if there was a difference in the proportion had an astigmatism.
Could this researcher have studied whether the gene variant causes increases risk of
astigmatism using an experimental design?
Yes, as a Confounder
Yes, as a Mediator
No, it does not explain the link
7
8
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Feedback
Based on answering correctly
Good choice! The explanatory factor we’re studying is a gene variant. But we can’t assign people to have a gene variant or not. We can only observe outcomes of people who happen to have the variant and people who don’t.
1 / 1 point
Let’s say that the researcher finds that people with the gene variant are more likely to
have an astigmatism. What could we reasonably conclude from this finding?
Feedback
Based on answering correctly
Nice job! Since this is an observational study, we cannot confidently assume causality. All we have done is notice an association between the two. There could still be another confounder here that explains why both the gene variant and astigmatism commonly occur together. For example, maybe this gene variant commonly occurs with another
gene variant that is the actual cause.
Yes, with the right resources, this could be an experiment, and there are no ethical
dilemmas here
Yes, but it would not be ethical based on the potential for harm of the response
variable
No. It’s not possible to assign people to the explanatory factor in this
investigation
The gene variant does not give us any indication of whether an astigmatism is likely
present or not in a particular person
The gene variant is associated with increased risk for an astigmatism, but we
don’t know if it is causally related
The gene variant causes changes to the body that makes astigmatisms more likely
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1 / 1 point
Use this information to answer questions 10-11. A car safety expert reviews accident
reports to identify the relationship between the age of a driver and the severity of
accident injuries. Accidents involving younger drivers are associated with higher rates of
severe injuries.
The safety expert is considering the possibility that younger drivers are more likely to
engage in risky driving behavior (like texting), and whether that might explain the increase
in severe injuries. Does “risky driving behavior” help explain this link? If so, what type of
explanation is it?
Feedback
Based on answering correctly
Good deduction! This explanation is framed to say that younger people engage in more risky driving behavior, and that reckless driving then leads to more severe injuries. Thus, the age of the driver is beginning the causal chain in this explanation.
1 / 1 point
The safety expert decides to stratify the data by “vehicle type.” He notices that when
comparing younger and older drivers of the same vehicle types, severe injuries are still
more common in accidents with younger drivers—the differences are still the same. What
does this mean?
Yes, as a Confounder
Yes, as a Mediator
No, it does not explain the link
The researcher identified vehicle type as a confounder to this relationship
10
11
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Feedback
Based on answering correctly
Good job! After stratifying by vehicle type, the researcher still saw an association. This means vehicle type didn’t explain away the difference. That said, there may still be other confounders that explain this connection! For example, younger people may be more likely to live in urban regions that naturally have more risky driving conditions.
1 / 1 point
Researchers from the National Institute of Health surveyed nurses in hospitals and clinics
across the country. They asked several questions including: “Do you current work in a
clinic or hospital in a rural setting?” and “Do you expect to still work as a nurse 5 years
from now?” They were curious if nurses who work in rural settings may be less likely to
continue in their position as compared to nurses in more urban or suburban settings.
What type of study is this?
Feedback
Based on answering correctly
Good choice! This data is being collected at one point in time, rather than over time, The researcher has ruled out vehicle type as a confounder, but there may still
be other confounders worth checking
The researcher has evidence that driver age is causally linked to severe accident
injuries
An Experiment
A Cross-Sectional Study
A Cohort Study
A Case Control Study
12
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or through back-tracking previously collected data. The nurses weren’t recruited into the study based on their explanatory outcome or their response outcome (as far as we can tell).
1 / 1 point
An epidemiologist (someone who studies infectious diseases) is examining patients who
have been hospitalized due to a new strain of the flu. She compares these patients with
others who had the flu but did not require hospitalization and is looking for explanatory
factors that might reveal differences between these groups. One significant difference she
finds is that those who were hospitalized tended to be much older on average than those
who were not hospitalized.
What type of study is this?
Feedback
Based on answering correctly
Awesome! This study is first identifying people with a particular response (hospitalization), then looking for a potential causal agent. This study is also retrospective (common with case-control studies), meaning that we have to use records or additional patient surveying to identify possible causal factors.
1 / 1 point
Non-steroidal anti-inflammatory drugs (NSAIDs) may increase the risk for indigestion and
nausea, but it may depend on the specific drug used. To study this, a doctor assigns some
patients seeking a pain relief drug to take ibuprofen while others are assigned to take
An Experiment
A Cross-Sectional Study
A Cohort Study
A Case Control Study
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naproxen. Over 1 month, the doctor notes how many people in each group report
indigestion or nausea as a side effects.
What type of study is this?
Feedback
Based on answering correctly
Nice job! The doctor assigned units to a treatment in this study. This allows the doctor to eliminate a lot of potential confounders and isolate the drug as the only systematic difference. This is in contrast to an observational study, where we can only observe what people already do. In those studies, groups may be different in more ways than the explanatory variable.
1 / 1 point
If we have completed an observational study, is there any way we can attempt to
determine whether the explanatory variable is causally linked to the response?
Feedback
An Experiment
A Cross-Sectional Study
A Cohort Study
A Case Control Study
No, but we can always complete an experiment with the same variables instead.
Yes, but cautiously. We can stratify for possible confounders, but we they can
never be sure that we have accounted for all possible confounders
Yes. If the observational study has a large enough sample size, then a causal inference
is appropriate.
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Based on answering correctly
Wonderful choice! It would be nice if we could always run an experiment instead, but there are a lot of conditions for which assigning units would not be ethical or possible. However, researchers can try to collect other potential confounding variables (sometimes called “covariates”) to see if there is still evidence for a difference, even after controlling for these other factors. This is in part how researchers determined that smoking greatly increased the risk for lung cancer.
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