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The Basics of Sampling

The Basics of Sampling. How do you find out something from a large group where it is impossible or impractical to look at everyone /thing?. Pollsters predict which candidate will win an upcoming election. Traffic researchers report that more people are wearing seat belts.

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The Basics of Sampling

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  1. The Basics of Sampling How do you find out something from a large group where it is impossible or impractical to look at everyone /thing?

  2. Pollsters predict which candidate will win an upcoming election. • Traffic researchers report that more people are wearing seat belts. • Government crash tests produce safety ratings for automobiles. • A soft drink company asks people to taste-test a new flavor of soda. • A quality control inspector tests some of a factory’s products. What do these have in common? What do they have in common? pg 1.2

  3. So, what’s in the jar? What color is it? Lets take a sample! How big should it be? What’s in it guess on pg 1.3 How large a sample is needed? pg 1.4

  4. Relating Vocabulary to the Jar • The jar represents a population. – the whole • What are they & what colors are they – are the population parameters. • Dumping it all out so we could see everything would be a census.

  5. Relating the jar to sampling. • The small cup is a sample – a small part of the population. • What are they & what colors are they in the sample – are the sample statistics. • How confident are you in the sample? Are you willing to bet your share of the contents on the sample?

  6. So, what’s in the jar? What color is it? Confidence in sample pg 1.6 Based on sample – what ‘s in it 1.7 How close was the sample pg 1.8 How good was the sample? Why?

  7. Mixing it up! Always possible to mix it up? Pg 1.9 Ways to mix up a population pg 1.9 But How?

  8. Randomizing! Selecting pieces at random from the population does the same thing as mixing it up! Everyone has a equal chance Of being selected No rhyme or reason for selections –

  9. What about Sample Size How big should the cup be? Should it be a percentage of the whole? 5%, 10%, 25% more? Population size does not determine sample size How large should sample size be pg 1.10 Does population determine sample size pg 1.11

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