Understanding Sampling

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Understanding Sampling

• Lesson 3-5

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Statistics, Data Analysis, and Probability (SDAP)
2.1
Compare different samples of a population with
the data from the entire population and identify
a situation in which it makes sense to use a
sample. Your Lesson Comparing Sampling
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Key Vocabulary
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Sampling

• The process of gathering data that can be used to
  predict the results of a particular situation.

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Population

• The entire group of people or things being
  considered in a statistical study.
• In statistics, population is NOT about all of the
  people living someplace
• Population is ONLY about the particular group of
  people or things you need answers from.

Entire means all everyone the whole thing
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Sample

• A part of the population
• A set of data from a part of the population that
  can be used to predict the results of a
  particular situation.

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About Sampling
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When would you use the entire population?

• When a group is small
• The ten biggest waterfalls
• When a whole group is easy to get to
• A class
• When the information from EVERYONE is easily
  collectedeven if the population is big
• Election results.
• If everyone is counted, then information is
  gathered from everyoneand all votes count

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When would you use a sample?

• The entire population is too big
• Every person in a housing complex, city, county,
  etc.
• A big barrel of marbles
• All of the soil in Southern California
• Ants, birds, fleas, all of any species
• You do not have access to everyone
• Every student at RCMS
• Checking every item would damage too many goods
  and make them unusable
• Every box of raisin bran cereal

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Lets look at a couple of situations and see why
it would be best to use a population or a sample
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• What or who is the population being studied?
• Was a population or a sample used to get this
  information?
• How do you know?

• According to a 1994 survey, 79 of the adults in
  California have completed high school.

ALL
SAMPLE!
SAMPLE There is no way to get to EVERY adult in
California! There are WAY TOO MANY adults in
California, plus people move in and out of the
state.
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• What or who is the population being studied?
• Was a population or a sample used to get this
  information?
• How do you know?

• The mean elevation of the ten tallest mountains
  in California are 14,196 feet.

POPULATION!
POPULATION Ten is a manageable number. You
should be able to find all of the elevations on a
map.
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Lets Practice
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• What or who is the population being studied?
• Was a population or a sample used to get this
  information?
• How do you know?

• Maria wants to know the mean height
• of her cats new kittens.

POPULATION!
POPULATION It would not be difficult to measure
the height of one cats new kittens.
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• What or who is the population being studied?
• Was a population or a sample used to get this
  information?
• How do you know?

ALL

• Brett read in an almanac that teens in the United
  States watch more than 12 hours of television per
  week.

SAMPLE!
SAMPLE There is no way to get to EVERY teenager
in the United States! How could anyone possibly
talk to ALL of them?
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• What or who is the population being studied?
• Was a population or a sample used to get this
  information?
• How do you know?

• Marisol recorded the scores of her math quizzes.
  She concluded that the average score was 86.5.

POPULATION!
POPULATION It would not be difficult to keep
track of her own quizzes.
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• What or who is the population being studied?
• Would you use a population or a sample?
• Why?

• You want to find the average height of a redwood
  tree in the 120,000 acre Redwood National Park.

all redwood trees in
SAMPLE!
SAMPLE EVERY tree in Redwood National Park?
There are 120,000 acres of trees! Have you ever
seen these redwood trees? Lets take a look
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Redwood National Park See the people? See the
trees? 120,000 acres of this? Need I say more?
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• What or who is the population being studied?
• Would you use a population or a sample?
• Why?

• You want to find the percent
• of students in the school band.

ALL
POPULATION!
POPULATION The office would know exactly how
many students are in band, and how many students
are in the entire school. This information is
relatively easy for you to get.
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• What or who is the population being studied?
• Would you use a population or a sample?
• Why?

• You want to find the mean height of all middle
  school students in California.

SAMPLE!
SAMPLE There are too many people and no way for
you to guarantee that you will get information
from all of them!
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• What or who is the population being studied?
• Would you use a population or a sample?
• Why?

• You want to find what percent of cars on
  California highways have out of state license
  plates.

ALL
SAMPLE!
SAMPLE 1) There are far too many cars on
California highways and you cannot get to them
all 2) there are too many highways 3) cars are
moving, you might count one twice
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• What or who is the population being studied?
• Would you use a population or a sample?
• Why?

• You want to find the average height of
• the members of the RCMS basketball team.

ALL
POPULATION!
POPULATION It would be easy enough to go to a
practice and collect the heights of the players
(with a coachs permission, of course).
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• What or who is the population being studied?
• Would you use a population or a sample?
• Why?

• You want to know what percent of the fortunes in
  a shipment of fortune cookies contain
  predications about wealth.

ALL
SAMPLE!
SAMPLE The fortunes are inside of the cookies!
If you opened up every cookie in a shipment to
see the fortunes, then the cookies are worthless.
No one would buy them and it would waste the
companys money or cost you A LOT to buy all of
them!