Transcript Module 12 Lesson 1 Notes

Notes
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A population is a large group of individuals you
want information about.
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An individual is defined to include people,
animals, or objects that are described by data.
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Realistically, though, would we able to survey
everyone in the United States to find out
something?
For example, could we ask every American what
their favorite food is or who they plan to vote for
in an election?
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A CENSUS
◦ a survey of an entire
population
◦ very expensive
◦ time-consuming
Example: US Census every 10 years
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A SAMPLE
◦ a group chosen to
represent an entire
population
◦ less expensive
◦ can be designed to take
much less time than a
census
Example: A phone poll asking who
you will vote for in an upcoming
election
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What is the population?
◦ The population is the
group of 250 computers.
Population = entire
group

What is the sample?
◦ The sample is the group
of 25 computers he
inspects.
Sample = chosen group

Convenience Sample: chooses individuals
who are easiest to reach
◦ Example: asking people leaving a grocery store
who they are going to vote for in an election
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Voluntary Response Sample: individuals
respond to a general request
◦ Example: people respond to a survey they received
in the mail
In other words, they are
biased.

A population might be UNDERREPRESENTED.
◦ one or more parts of a population are left out when
choosing the sample
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A population might be OVERREPRESENTED.
◦ an emphasis is placed on one or more of the parts
of a population
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A survey is conducted
by calling 100 people
randomly chosen from
the phone book and
asking them what their
favorite kind of
toothpaste is.
Scenario #1

A restaurant owner
wants to know how
often families in his
area go out for dinner.
He surveys 30 families
who eat at his
restaurant on Tuesday
night.
Scenario #2

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The random people
chosen from the phone
book are not
necessarily
representative of the
entire city’s
population.
People who aren’t
listed in the phone
book are excluded.
Scenario #1 is BIASED
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The sample is a
convenience sample,
which probably isn’t
representative of the
entire area’s
population.
Families already eating
out may eat out more
often than other
families in the are.
Scenario #2 is BIASED
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Imposes a treatment
on individuals
Collects data on their
response to the
treatment

Observes individuals
and measures variables
without controlling the
individuals or their
environment in any
way

A researcher asks
students the average
number of hours they
spend studying for a
test to see if there is a
relationship between
studying and grades.
This is an observational
study, because the
researcher isn’t
controlling the students
or applying a treatment.
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A cosmetologist wants
to know whether nail
polish A lasts longer
than nail polish B, so
she paints two sets of
nails with each polish.
This is an experiment,
because the
cosmetologist applies a
treatment to some
individuals.
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For experiments to be useful, they must be
carefully thought out and designed.
A CONTROLLED EXPERIMENT sets up a control
group and a treatment group so that two
groups can be studied under conditions that
are identical except for one variable.
A RANDOMIZED COMPARATIVE EXPERIMENT is
one in which individuals are assigned to the
control group or the treatment group
randomly in an effort to minimize bias.
At a local elementary school, 150 randomly
chosen students were given milk at lunch for
a year. 150 other randomly chosen students
were given other drinks at lunch for a year. At
the end of the year, students in the milk
group had 22% fewer calories than the students
in the other group.
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Randomized Comparative Experiment
Treatment is drinking milk at lunch
Treatment group drank milk
Control group drank other beverages
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Which would be better: an experiment or an observational
study?
In this case, an observational study would be best,
because it wouldn’t be fair to ask a treatment group to
possibly ruin its hearing if the individuals don’t already
listen to music with headphones.
To be effective, randomly choose one group of people that
already listens to an iPod™ with headphones for more than
two hours a day. Then, randomly choose one group of
people that doesn’t listen to music with headphones.
Monitor the hearing of both groups regularly and record
results.