Sampling

1
Sampling Bias

• Vocabulary Practice

2
Unbiased Random

• 3 Types of Random Samples
• Simple
• Truly random sampling of whole population
• Example Draw names from a hat
• Stratified
• Simple random sample within equal divisions of
  population
• Example Draw 3 random students of each grade
• Systematic
• Interval of time or items
• Example Every 10 seconds or every 15th bottle

3
Biased

• 2 Popular Forms of Biased
• Convenience Sample
• Survey whats handy
• Example Kittens at veterinary
• Voluntary Response
• Only those who chose to participate
• Example Survey those who answered ad

4
Practice

• A shopping mall wants to know if they should put
  a movie theater in the mall. Every hour, the mall
  manager questions 20 of the people coming into
  the mall.
• Identify the sample and suggest a population from
  which it was selected.
• Classify the sample as simple, stratified, or
  systematic.

5
Answers

• The sample is a group of shoppers at the mall, 20
  every hour. The population is all mall customers.
• This is a systematic random sample. The people
  questioned are chosen according to a time
  interval.

6
Practice

• A sub sandwich store owner wants to make sure
  that his employees are weighing the meat
  correctly to put on the sandwiches. He watches
  the meat being weighed for one hour during the
  day.
• Classify the sample as biased or unbiased.

7
Answer

• The sample is biased since he is watching only
  one employee for only one hour during the day.

8
Practice

• A fast food restaurant is testing a new food
  item. To test if the customers are satisfied, the
  store owner asks the first 15 customers of the
  day if they would purchase the item.
• a. Identify the sample and suggest a population
  from which it was selected.
• b. Classify the sample as a convenience sample or
  a voluntary response sample.

9
Answers

• The sample is the first 15 customers of the day
  at the fast food restaurant. The population is
  all customers of the fast food restaurant.
• Since this involves a population that is easily
  accessed, this represents a convenience sample.

10
Practice

• A state tourist board wants to determine the
  states favorite camping sight. They send a
  survey to all mailing addresses to be filled out
  and mailed back to them.
• Identify the type of sample.

11
Answer

• This is a voluntary response sample. Only those
  that want to participate in the survey will mail
  their response back.

12
Your Turn

• In class, with your partner do Page 711 (8, 10,
  16, 19, 20)
• Well correct in class in 10 minutes.

13
Answers

• 8 Unbiased, Simple
• 10 Biased, Convenience
• 16 Biased, Voluntary
• 19 Unbiased, Systematic
• 20 Unbiased, Stratified