Scientific writing (81-933)
Lecture 5: Discussion
Dr. Avraham Samson
Faculty of Medicine in the Galilee
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THE DISCUSSION
The Discussion is the section that…
• Gives you the most freedom
• Gives you the most chance to put good writing
on display
• Is the most challenging to write
The Discussion
The purpose of the discussion:
•
•
•
•
Answer the question posed in the Introduction
Support your conclusion with details (yours, others)
Defend your conclusion (acknowledge limits, caveats)
Highlight the broader implications of the work (i.e., What
do my results mean and why should anyone care?)
• Future plans (optional).
• Strong conclusion
The Discussion
The introduction moves from general to specific.
The discussion moves from specific to general.
The Discussion
Things to avoid in the discussion:
• Do not simply repeat what is in the Results
• Do not try to explain every minor flaw
• Do not attempt to explain away every
unexpected result
• Do not exaggerate or make extravagant claims
• Don’t hedge
What NOT to do!
Don’t start your discussion like this!!
Discussion
• This meta-analysis is subject to a number of
limitations. The estimates of risk for melanoma
subsequent to using sunlamps/sunbeds are based on
published data in a series of 10 articles over a period
of 20 years. A pooled analysis of original
observations taken in the 10 studies would have
provided a more powerful approach …
The Discussion: verb tense
Verb Tenses (active!):
Past, when referring to study details, results, analyses, and background
research:
•
We found that
•
They lost more weight than
•
Subjects may have experienced
•
Miller et al. found
Present, when talking about what the data suggest …
The greater weight loss suggests
The explanation for this difference is not clear.
Potential explanations include
EXAMPLE: Adherence to Mediterranean diet and risk
of developing diabetes: prospective cohort study
BMJ June 2008
END OF INTRODUCTION:
We evaluated the association between
adherence to a Mediterranean diet and the
incidence of diabetes using a full validated
food frequency questionnaire to measure
the entire diet.
The Discussion
1. This large prospective study shows that a
traditional Mediterranean food pattern is
associated with a significant reduction in the
risk of developing type 2 diabetes. [answer to
question asked]
The Discussion
2. Interestingly, among participants with the highest adherence to the diet, there was a high
prevalence of important risk factors for diabetes, such as older age, higher BMI, family
history of diabetes, and personal history of hypertension and a higher proportion of exsmokers. Therefore, we would have expected a higher incidence of diabetes among these
participants. These higher risk participants with better adherence to the diet, however, had
a lower risk of diabetes, suggesting that the diet might have a substantial potential for
prevention. [“bonus” finding/additional evidence] This finding is consistent with our
previous report of an inverse association between a Mediterranean diet and the metabolic
syndrome.24 [fits with previous research] The metabolic syndrome is closely associated
with a generalised metabolic disorder of insulin resistance, which is one of the underlying
causes of type 2 diabetes. Therefore a high biological plausibility exists to support the
causality of our findings. [biological mechanisms] In addition, a previous cohort study of
survivors of myocardial infarction also reported that a higher adherence to a Mediterranean
diet was associated with a reduction in the risk of type 2 diabetes,18 [fits previous research]
despite use of a relatively inaccurate tool for the dietary assessment. The inverse graded
dose-response pattern and the significant inverse trend that we observed also support a
causal relation. [dose-response evidence]
The Discussion
3. Diet and disease.Experimental evidence suggesting that a diet similar to the
Mediterranean diet and rich in plant based foods might protect against diabetes
can also be found in the Indian diabetes prevention programme. That trial
promoted a plant based diet (together with increases in physical activity) and
found a significant reduction in the incidence of diabetes,28 although there are
clear differences between the Mediterranean and Indian food patterns. There is
an analogy between coronary heart disease and diabetes because patients with
type 2 diabetes and no coronary heart disease have a risk of coronary heart
disease similar to patients without diabetes but with prior coronary heart
disease.29 There is evidence that a Mediterranean diet protects against
coronary heart disease, and the analogy between coronary heart disease and
diabetes suggests that this diet might also prevent diabetes. It has been shown
to provide protection against coronary mortality8 9 30 31 and the incidence of
non-fatal myocardial infarction.32 In addition, both cohort studies33 34 35 and
randomised trials36 have found that adherence to a Mediterranean diet
protects against mortality in patients who already have established coronary
heart disease. [more supporting background evidence]
The Discussion
Limitations.
The number of new cases of diabetes was small, despite the follow-up of several thousand
people for over four years. This small number of incident cases is a major drawback and
can compromise the statistical power of our study. Nevertheless, our participants had high
absolute levels of consumption of the typical food items of the Mediterranean diet, even
among those participants classified as poorly compliant (score <3). For example, among
those in the lowest category of adherence to the diet, the estimated mean daily absolute
consumption (g/day) of olive oil (12), vegetables (308), fruits (176), cereals (77), and
legumes (17) can be considered as healthy for the standards of nutritional epidemiological
studies. This high consumption of plant based foods in our cohort could be because our
participants were from a Mediterranean country and were highly educated and health
conscious. The small number of new cases observed in this study should therefore not be
surprising. If the Mediterranean diet is actually protecting against diabetes, we would
expecta low incidence in a young cohort (mean age is 37.8 years) with these
characteristics. The low number of observed cases precluded assessment of the specific
role of single dietary factors because we would have needed
[Limitations]
The Discussion
•
Conclusion. Our prospective cohort study suggests that
substantial protection against diabetes can be obtained
with the traditional Mediterranean diet, rich in olive oil,
vegetables, fruits, nuts, cereals, legumes, and fish but
relatively low in meat and dairy products. The limited
number of cases of diabetes and the possibility of
under-reporting, however, requires that further larger
cohorts and trials are needed to confirm our findings.
[Restatement of the findings—take home message]
Discussion
1. The answer to the key question asked
2. What’s new
3. The context. How your results fit into, contradict, or add
to what’s known or believed
4. Strengths and limits of the study
5. Overall conclusion
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“Subject verb object”
“Subject verb object”
“Subject verb object”
“Subject verb object”
“Subject verb object”
Right!
• The Neanderthal man became extinct 30,000
year ago. Recently however, Neanderthal
genes were found in living humans. In
addition, Neanderthal features such as long
noses and light hair are commonly observed in
todays population. These findings suggest that
Neanderthals intermarried with Homo
Sapiens.
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Wrong!
• 30,000 years ago, the Neanderthal man was
extincted. In living human, genes of
Neanderthals were found. Also, Neanderthal
feature’s such as long nose and light hair are
commonly observed in today’s population.
Homo Sapiens and Neanderthals can
intermarry.
19
Principles of Effective Writing
Really long
subject!
“The fear expressed by some teachers that
students would not learn statistics well if they
were permitted to use canned computer
programs has not been realized in our
negatives
experience. A careful monitoring of
achievement levels before and after the
introduction of computers in the teaching of
our course revealed no appreciable change in
students’ performances.”
wordy
Passive
voice
Principles of Effective Writing
“The fear expressed by some teachers that
students would not learn statistics well if they
were permitted to use canned computer
programs has not been realized in our
experience. A careful monitoring of
achievement levels before and after the
introduction of computers in the teaching of
our course revealed no appreciable change in
students’ performances.”
Buried predicate
+ boring verb
“hedge” word
Really long
subject!
Principles of Effective Writing

“Many teachers feared that the use of canned
computer programs would prevent students
from learning statistics. We monitored student
achievement levels before and after the
introduction of computers in our course and
found no detriments in performance.”
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24
1. Peremptory v. preemptive
Peremptory = cannot be denied
Preemptive = action is one taken before an adversary
can act
He issued a peremptory order.
He ordered a preemptive war in Iraq.
2. Subject v. patient
A subject is a volunteer.
A patient is under treatment by a doctor.
The subjects in our study took a quiz about love.
The patients in our study were being treated for their
stomach conditions.
Alternatives to “subject”: participants, volunteers, men,
women, postmenopausal women, runners, smokers,
etc.
3. Strata v. stratum
“Strata” is plural.
“Stratum” is singular.
We analyzed the data, adjusting for the different age
strata.
I was only interested in the association in the stratum
of elderly subjects.
4. Nucleus v. nuclei
“Nuclei” is plural.
“Nucleus” is singular.
The cell nucleus displayed a pattern of
chromosome abnormalities.
Proton nuclei in different chemical
environments display distinct precession
frequencies
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5. Averse v. adverse
Averse means “opposed” and usually describes a person’s
attitude.
Adverse means “hostile, unfavorable, opposed” but usually
applies to situations, conditions, or events—not
people.
The bad weather has an adverse effect on my car.
I would not be averse to trying that new restaurant.
6. Historic v. historical
Historic means notable in history.
--indicates that it in some way changed the course of
human events
Historical means relating to history or past events.
--not necessarily historic
The signing of the Declaration of Independence was a
historic moment in American history.
Professor Smith gave a historical lecture on the evolution of
toothpicks.
7. Ultimate and Penultimate
Ultimate: last (from Latin, ultimare=“come to an end”)
Penultimate: second to last (paene=“almost”;
ultimas=“last”)
The ultimate aim was to force his resignation.
The character was arrested in the penultimate chapter,
setting up the central tension of the final chapter.
Re: Letter Of Reference
To: John Doe
To Whom It May Concern:
Bob Smith, my assistant programmer, can always be found
hard at work in his cubicle. Bob works independently, without
wasting company time talking to colleagues. Bob never
thinks twice about assisting fellow employees, and he always
finishes given assignments on time. Often he takes extended
measures to complete his work, sometimes skipping coffee
breaks. Bob is a dedicated individual who has absolutely no
vanity, in spite of his high accomplishments and profound
knowledge in his field. I firmly believe that Bob can be
classed as a high-caliber employee, the type which cannot be
dispensed with. Consequently, I duly recommend that Bob be
promoted to executive management, and a proposal will be
executed as soon as possible.
Received a short time later:
Re: Letter Of Reference
To: John Doe
Mr. Doe:
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That idiot was standing over my shoulder while I wrote the letter I sent to you earlier today. Kindly
re-read only every other line.