Lecture slides for Day 13 in EWRT 2

1. EWRT 2
Day 13
STATISTICAL LITERACY

2. Business / Participation
The paper syllabus you originally received is now
significantly outdated. Always check the
electronic copy from here on out.
Paper 2 due today by 6 PM on Canvas.
Journal 4 due at the end of this week. We will go
over it in detail a bit later today.
Next week: I won’t see you! 
How did data collection go? Integrated Project
due this week.
Participation for today
◦ 2 points for arriving on time.
◦ 2 points: one individual, one from group activity.

3. Library Skills and Journal 4

4. Statistics and Interpretation
Multiple people were interested in Levitin’s
assertion that “statistics are interpretations.”
But what does he mean here?
◦ does he mean the actual math is an
interpretation?
◦ are the calculations not objective?
Levitin (3): “People choose what to count, how
to go about counting, which of the resulting
numbers they will share with us, and which
words they will use to describe and interpret
those numbers.”
Example: Suppose I am interested in the link
between caffeine and anxiety and I want to do
a study and collect some statistics:
◦ what to count: say that I choose to count cups of
coffee as a measure of caffeine consumption.
How is that potentially an “interpretation”?
◦ how to go about counting: say that I ask people
to report how many cups of coffee they drank
this week and how anxious they felt (on a scale
of 1-5). How is this potentially an interpretation?
◦ which numbers to share: say that I report the
mean of 2.4 cups of coffee. How might this be an
interpretation?
◦ which words to use: say that I find say that I find
a strong correlation between coffee and anxiety
and I claim that “caffeine causes anxiety.” How is
this an interpretation?

5. How can we use our common sense and basic
math skills to come up with plausible estimates?

6. Fermi Estimates
Named after physicist Enrico Fermi, physicist on the Manhattan Project (atomic bomb).
“Quick and dirty” estimates.
Idea is not to get it perfect, but to get within a power of ten
(which isn’t incredibly close, but often close enough).
Combination of background knowledge and reasonable guesses.
I find that three pieces of information can often help with this:
◦ population of the world: 7.5 billion
◦ pop. of the US: 320 million
◦ pop. of California: 40 million
Practice makes these easier.

7. Fermi Estimate Practice Problems
In (new) groups!
Six examples—some have a real answer, some don’t.
We’ll do two of them together. No internet allowed, but calculators are okay.
If you want to look up a number, ask me.
1. How many miles does a person walk in a lifetime?
2. How many new passenger cars/trucks are sold each year in the USA?
3. How much does the California state government spend on K-12 education every year?
4. If an airline asked its passengers to urinate before boarding the airplane, how much fuel (by
percent) would the airline save per flight?
5. On average, how many people are airborne over the US right now?
6. On any given day, how many people go surfing in California?