The Midterm Exam
HW 2 Again
Stress and Headaches
“In the study, researchers… found
that the greater the stress in a
person's life, the more intense
and frequent their headaches
were.”
Correlation
A = amount of stress
B = strength and number of
headaches
A is positively correlated with B
B is positively correlated with A
Explanation for Correlation
Possible causal structures:
• A causes B
• B causes A
• Some other variable C causes
both A and B.
Researcher’s Explanation for Correlation
Possible causal structures:
• A causes B
• B causes A
• Some other variable C causes
both A and B.
Explanation for Explanation
Stress causes headaches.
↑
Why?
The Article Does Not Say!
“Although headaches can be
triggered by many factors, ranging
from muscle strain to exposure to
noxious gases, stress clearly plays
a major role.”
Clearly? Why?
Posit a Mechanism
• Stress causes an increase in the
hormone adrenaline.
• Adrenaline opens blood vessels
for faster flowing blood, and
quicker reaction.
• Elevated levels of adrenaline
over long times can cause the
blood vessels in the head to
send pain-signals to the brain.
• That’s why Stress causes
headaches.
Facebook and Body Image Problems
“Female students who spend a lot
of time on the social networking
site tend to be more body
conscious and to suffer from more
anxiety.”
Facebook and Body Image Problems
“They also tend to give greater
significance to the number of
comments and ‘likes’ on their
pictures and status updates.
They are more likely to ‘untag’
themselves in pictures.”
Correlation
A = time that young women spent
looking at pictures on facebook
B = unhealthy body image
A is positively correlated with B
B is positively correlated with A
One Explanation
A→B
Looking at pictures longer on
facebook causes an unhealthy
body image in young women.
Mechanism
A→X→B
Looking at pictures longer on
facebook causes women to
compare themselves with others
and this causes an unhealthy body
image.
NOT a Different Explanation
A→X→B
Providing a mechanism is not the
same thing as providing a different
explanation for the correlation.
This is still the A → B explanation.
Tracing Causes Back
X→A→B
Having easier access to computers
causes looking at pictures longer
on facebook, which then causes
an unhealthy body image in young
women.
NOT a Different Explanation
X→A→B
Tracing the causes back further is
not the same thing as providing a
different explanation. Here we are
still assuming that A causes B, we
are just explaining what causes A.
Widening the Target
X
A→B
Facebook and twitter and
instagram and tublr and… all
cause looking at pictures longer
on, which then causes an
unhealthy body image in young
women.
Also NOT a Different Explanation
X
A→B
Again, this explanation still says
that A causes B, it just lists a
bunch of other causes of B.
Sex and Money
“[P]eople who had more money,
reported more sexual
satisfaction.”
Sex and Money
“[P]eople who had more money,
reported more sexual
satisfaction.”
Sex and Money
A = socioeconomic status ($$$)
B = sexual satisfaction
A is positively correlated with B
B is positively correlated with A
Tracing Back the Causes
X→A→B
Being educated causes one to
acquire wealth. Wealth attracts
better sexual partners.
True Common Cause
A←C→B
Being educated causes one to
acquire wealth. Being educated
also causes one to have a better
awareness of one’s need and thus
to have better sex.
Doesn’t Always Make Sense
A←C→B
Living in a prosperous country
causes one to acquire wealth.
Living in a prosperous country also
causes one to have a better
awareness of one’s need and thus
to have better sex.
Doesn’t Always Make Sense
A←C→B
Everyone in the study was from
Spain!
Midterm Exam
Problem #1
After the nuclear disaster at
Fukushima, lots of people rushed
out to buy iodized salt. These
people thought that “three men
make a tiger” and if enough
people say something is true, then
it is. This is just the appeal to
popularity, and it is a bad way to
form your ideas.
Problem #1
That is why I know that iodized
salt does not protect from nuclear
radiation.
Based on the information we
learned in class, what is the main
flaw with this argument?
The Fallacy Fallacy
This is a bad argument:
1. You have presented argument A for your claim C.
2. A is a fallacious argument.
3. Therefore, C is false.
Problem #2
Imagine that a school decides to try a new way to teach reading to its
students. They use the new teaching method over an entire term and
discover that 80% of the students test better in reading proficiency at
the end of the term, compared with how they tested at the beginning.
The school concludes that the new way of teaching reading works, and
they decide to keep using it in the future.
Based on the information that we learned in class, what is the main
problem with the conclusion the school reaches? What should they
have done instead?
There’s No Control Group
Of course students will get better at reading after an entire year of
teaching.
What we want to know is whether the new method works better than
the old method.
So we need two group: the experimental group using the new method
and a control group using the old method.
Problem #3
Neglecting to follow a dentist’s
directives can lead to heart
disease, high blood pressure, and
stroke — and that’s only a glimpse
of the possible adverse effects of
ignoring the importance of good
oral health.
Problem #3
“The scary part is that 40 percent
of people with heart conditions
have gum disease,” Dr. Kabour
said.
“The big question they ask is how
it happens: Bacteria that grows on
the gums affects the inner layer of
the heart, which builds up plaque
over the years.”
Problem #3
• According to this story, which
two variables are correlated?
• What is the researcher’s
explanation for the correlation?
• Please offer an explanation of
the correlation that differs from
the one provided by the
researcher.
Correlation
A = gum disease
B = heart disease
A is positively correlated with B
B is positively correlated with A
Researcher’s Explanation
There’s a common cause: gum
disease is caused by bacteria that
grows on the gums.
This bacteria also affects the
heart, and causes it to build up
plaque over many years.
Correlation
A = doing what the dentist says
B = heart disease
A is negatively correlated with B
B is negatively correlated with A
Researcher’s Explanation
A causes B. Not doing what the
dentist says causes bacteria to
grow on your gums. This bacteria
then affects the heart, and causes
it to build up plaque over many
years.
Alternate Explanation
There’s a common cause: sugar.
Consuming sugar causes bacteria
to grow on your gums and then
causes gum disease.
But tooth-decay is NOT what
causes heart problems. The sugar
does. Sugar causes weight gain
and this strains your heart.
Researcher’s Explanation
You can tell this is a different
explanation because what it
recommends is different.
Good oral hygiene will not prevent
heart disease, if this explanation is
true: only removing sugar from
your diet will.
Problem #4
Using figures from the last election, researchers discover that districts
in Hong Kong that were wealthier (higher average income) were also
districts that voted more for pro-democratic politicians from the Civic,
Democratic, and People Power parties. Districts that were poorer voted
more for pro-Beijing politicains from DAB, FTU, and NPP.
Using the information that we learned in class, explain why these
results should not lead us to believe that wealthier people are more
likely to be pro-democratic.
Blue = Democrat
Green = $$$
Ecological Fallacy
States with the highest average incomes have a higher percentage of
democratic voters.
So does this mean that people who are wealthy are more likely to vote
democrat?
No! The opposite is true.
Nanotips
Gloves that work with
touchscreens aren’t new, but
they’re usually sold at a premium
and have to be bought separately
from your existing gloves.
Nanotips
A new technology claims to solve
this problem by letting you turn
any pair of ordinary into
touchscreen ones simply by
painting the fingertips with a
special liquid. Called Nanotips, the
liquid is made of conductive
polyamide that soaks into the
fabric and builds a conductive
'bridge' between your finger and
the screen.
Nanotips
A Nanotips pack costs $20 (£12)
but can be used on multiple
gloves. Shipping costs $3.50 and it
is due to go on sale on 20 March.
The company does ship
internationally.
It’s an advertisement disguised as news!
http://www.dailymail.co.uk/sciencetech/article-2580983/Now-ANYgloves-work-touchscreen-12-paint-transforms-woolly-fingertipsprosthetic-limbs.html
Hints
• Detailed description of the product
• No discussion of alternatives
• Pricing information
• Information about international shipping
How is any of that news?
Ah Shi Point Acupuncture
Ah shi point acupuncture involves
inserting needles at painful places
on the body, unlike regular
acupuncture.
Problem #6
http://www.ncbi.nlm.nih.gov/pubmed/20813813
Here is a description of a scientific experiment on ah shi point
acupuncture as a treatment for acne: 36 subjects were randomized in a
double-blind controlled trial. The control group received acupuncture
at general acupuncture points only, and the experimental group
received acupuncture at both general acupuncture points and ah shi
points.
Problem #6
The study involved 12 acupuncture sessions over six weeks. It found
there was a significant reduction in the amount of acne in both groups,
but the experimental group did not do better or worse than the control
group. The researchers concluded that acupuncture was an effective
treatment for acne.
Based on the information that we learned in class, what is the main
reason this scientific study does not support the researchers’
conclusion?
No Controls, Again
There was no no-acupuncture/ fake acupuncture control group.
This study shows that ah shi point acupuncture does not work better
than regular acupuncture.
It does not show that acupuncture works better than no-acupuncture,
because there was no no-acupuncture/ fake acupuncture control
group. Maybe all three groups would have improved equally.
Problem #7
The Malaysian prime minister once made the following argument: It is
bad to give successful Malaysian badminton players lots of money and
fame when they achieve great international success. Every player that
has achieved great international success, and then been given lots of
money and fame, has gone on to play worse in their next tournament.
Based on the information that we learned in class, what is the main
flaw in the prime minister’s argument?
Regression to the Mean
Whenever two variables are imperfectly correlated, extreme values of
one variable tend to be paired with less extreme values of the other.
Regression Fallacy
The regression fallacy is when you attribute a cause to a regression
effect.
“Jeremy Lin lost after appearing on Sports Illustrated. A curse!”
The Sports Illustrated Jinx
For example, while this
was the cover of SI in
February, Jeremy Lin shot
1-for-11 in a game where
the New York Knicks lost
to the Miami Heat 102-88.
Malaysian Badminton Players
When do badminton players receive fame and money? When they are
doing unusually well.
Subsequently they regress to the mean and do less well. It’s not
because they got fame and money, it’s because whenever two variables
are imperfectly correlated, extreme values of one variable tend to be
paired with less extreme values of the other.
Problem #8
It is natural for women to have
children.
All female animals are designed to
reproduce their species.
The only reason any of us exists is
because our mothers birthed us
into this world.
Problem #8
Therefore it is wrong for women
to choose to have careers instead
of having children, and it is wrong
that our society so often forces
women to work instead of staying
home and having children.
Problem #8
Based on the information we
learned in class, what is the main
flaw in this argument?
Appeal to Nature
The appeal to nature fallacy is when someone argues that something is
true/ good because it’s natural or when they argue that something is
false/ bad because it’s unnatural.
Problem #9
Grand Theft Auto V is one of the
best-selling video games of all
time.
It was available on two video
game consoles: Sony’s Playstation
3 (PS3) and Microsoft’s Xbox 360.
More people purchased the game
for PS3 than for Xbox 360.
Problem #9
Based on the information we
learned in class, explain why the
following chart is misleading.
Some Things to Note
• It’s a truncated chart.
• The Y-axis does not start at zero.
• The chart exaggerates the
difference in preference
between the PS3 and the Xbox
360.
• The real difference is 3%.
• The portrayed difference is
200%.
Video Time!
http://www.economist.com/multimedia?bclid=1294626183001&bctid
=2719450974001
Problem #10
Science tests hypotheses about the causal structure of the world. Only
about 1 in 10 hypotheses are true. This is because, for example, there
are more things that do not cause cancer than things that do cause
cancer. So most hypotheses about the causes of cancer will be false.
Only 1 in 10 hypotheses are true.
Problem #10
Suppose I conduct an experiment to test the hypothesis that A causes
B. The results of the experiment seem to confirm the hypothesis. I
know that if A does cause B, then I would get these results 95% of the
time…
95% of true hypotheses test positive.
That’s these ones.
Problem #10
…and if A does not cause B, I would get these results only 5% of the
time.
5% of false hypotheses test positive.
That’s these ones.
Problem #10
Given the information that we learned in class, how certain should I be
that A causes B? Please explain your answer.
High proportion of false positives.
Answer
There’s only about a 64% chance that the correlation I found is due to
true hypothesis.
Base Rate Neglect Fallacy
The base rate neglect fallacy happens when:
1.
2.
3.
4.
There is a low base rate of some condition.
We have a test for that condition.
Someone tests positive.
We assume that means they have the condition, ignoring the
unreliability of tests for conditions with low base rates.
Importance of Base Rates
As the base rate decreases, the proportion of false positives out of total
positives increases:
False Positive
÷
False Positive + True Positive