Self-study
Commentator: The reported epidemic of childhood obesity in our country is a myth. ████ ███ ████ █ ██████ █████ ███ ████ █ █ █████ █████ █████████ ████████ ██ ██████████ ███████ ███████ ████ ██ ███ █ ███████████ █████████ ██ ███ ██████████ ██ ████████ ███ ███ █████ ██████ ████ █████████ ██████████████
Method of Reasoning
The argument proceeds by citing a statistical average to support a conclusion about how the increases are distributed across individuals. Because the average weight of a child has only increased slightly, the commentator concludes that there must not be a substantial increase in the percentage of children who are obese.
Identify and Describe Flaw
The commentator assumes that a small change in average weight means there hasn’t been a big increase in the percentage of children who are obese. However, this represents a misunderstanding of how averages work: a small change in the statistical average does not necessarily reflect how weight changes are distributed across individuals. Even if the average weight only goes up a little, the proportion of obese children could still increase a lot.
For example, if 1% of children were obese before and now 3% are, then the proportion of obese kids tripled—even if the average weight barely changed. Or what if 15% children became obese, while the remaining 85% lost weight? That could balance out to only a small average increase, despite a large increase in obesity.
15.
Which one of the following ████████ ██████ █████████ ████ ███████ ██ ███ ██████ █████████ █████████ ██ ███ ████████ ██████
a
The average summer ███████████ ████ ███ ████ ████ █████ ████ ████ ██████████ █████ ████ ██████ ███████ ████ ███████ ███ ███████ ███████
Wrong flaw. This supports a factual claim about the past with a premise that describes what most people believe. The stimulus doesn't rely on people's beliefs as evidence.
b
The proportion of █████████ ███ ████ ████ ████ ████████ ████ ███ ████ █████████ ████ ████ ████████ ████ ███ ████ █████ █████ ███ ███████ ██████ ███ █████████ ████ ████████ ████ ████ █████
(B) assumes that a small change in average salary means there hasn’t been a big increase in the percentage of employees who earn high salaries. This matches the flaw in the stimulus. And like in the stimulus, since averages don’t tell us how changes are distributed, it’s possible that the proportion of high-earners increased substantially despite the average not changing much.
c
The proportion of █████████ █████████ ██ ███ ████████ ████ ████ ████ █████████ █████████████ ██ ██████ ██████ █████ █ ███████████ ██████ ██ ██████ █████████ ████ ████ █████████ ██ █████████ █████████ ██████ ████ █████
Wrong flaw. This assumes that there hasn’t been a substantial number of new non-apartment buildings built in recent years. The stimulus improperly cites an average to support a claim about how a change is distributed across individuals, whereas (C) doesn't involve a statistical average.
d
The average weight ██ ██████ ████ ████ █████████ ██ ███ ████ ███ ██████ █████ ███████████ ████ █████████ ███ ██████████ ██ ████████████ ██████ ██ █████ █████ ██ ██████ ██████
Wrong flaw. This assumes that a change in restaurant menus must cause a change in adults’ weights. Put differently, (D) baselessly assumes a causal relationship. That's distinct from the stimulus, which uses a statistical average to support a claim about a distribution across individuals.
e
The average price ██ █ █████ ████ ██ ███████████ █████ ███ ██████████ ██ █████████ ██████ █████ ██ ███████ ███ █████████ ████ ███ ████ █████ ██████
Wrong flaw. This assumes that a change in the proportion of income spent on housing must reflect a change in the average price of housing—it ignores other possible explanations, such as a decrease in income. The stimulus does the inverse, citing a change in the average to support a claim about proportion.