Making Predictions

1
Making Predictions

• Predict the actions of a larger group using a
  sample

2
Definitions

• Survey a method of collecting information
• Population the group being studied
• Sample a small part of the group or population
• Random Selected without preference

3
How many students in this school are left-handed?

• To answer that question we could
• Ask every student in the school OR
• We could survey a small random sample

If our sample is random it should be
representative of the population.
4
Our Survey

• Question Do you write left-handed or
  right-handed?
• Population All students at SDMS
• Sample Mr. Lovells 6th grade math class
• Is Mr. Lovells Math class a good choice?
• Selected without preference?
• Representative of the population?
• Large enough group to provide reliable data

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Make a prediction about the population
Based on the results of your survey, you can make
a prediction about the whole school.
Suppose 5 out of 20 students are left-handed.
The probability that a student is left-handed is
6
Our prediction
If the probability of a student being left-handed
is ¼ THEN ¼ of the population should be
left-handed.
There are 960 students at SDMS SO ¼ of 960 is
240Our predictions is
7
There are 240 left-handed students at SDMS

• If our sample is random, our prediction should be
  fairly accurate!

8
Determine a good Sample

• Every 9th person entering a grocery store is
  asked to state their choice in an upcoming
  election.
• One hundred people in an Italian restaurant are
  asked their favorite type of restaurant.
• Every 5th person attending a WMHS basketball game
  is asked their favorite High School

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Good Sample?

• Every 20th person leaving school is asked if they
  pack their lunch or buy a school lunch.
• Five people at a soccer match are asked their
  favorite sport.

10
Which Sample is Best?
Question Who is your favorite movie star?

• Ask people standing in line waiting to see a
  movie
• Ask people at a local shopping center

11
Survey and Prediction
Lauren asked every 4th student on an alphabetical
list of the Dream Team to name their favorite
pizza topping
12
What is the probability that a student likes
Meat-lovers pizza?
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P(Meat-lovers) 5/25 or 1/5
14
Prediction
If there are 300 6th grade students, how many
probably like meat-lovers pizza?
What is 1/5 of 300?
15
We predict that 60 students will prefer
meat-lovers Pizza.
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Remember to conduct a survey

• What is your population what group do you want
  to know about
• How do you pick your sample
• Is your sample random meaning picked without
  preference, representative of the population and
  big enough to provide accurate data.