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### 6.4 Select and draw conclusions from samples

GOAL: study different sampling methods for collecting data.

Sample: subset of the population

Self-selected sample, members of a population can volunteer to be in the sample.

Systematic sample, a rule is used to select members of a population, such as selecting every other person.

Convenience Sample, easy-to-reach members of a population are selected, such as those in the first row

Random Sample, each member of a population has an equal chance of being selected

Classify samples

Example 1:A teacher wants to find out how many hours students studied for a history quiz. Identify the type of sample described.

- Before leaving the room, the teacher asks students to write the number of hours they studied for the quiz on the chalkboard if they want to participate.
- The teacher selects students randomly from an alphabetical list and asks the selected students how many hours they studied for the quiz.

Self selected Sample

Random Sample

Overrepresent or

Underrepresent the population

Represents the population

Tell whether each the following samples are biased or unbiased

Example 2:

- A teacher wants to find out how many hours students studied for a history quiz.
- Before leaving the room, the teacher asks students to write the number of hours they studied for the quiz on the chalkboard if they want to participate.
- The teacher selects students randomly from an alphabetical list and asks the selected students how many hours they studied for the quiz.

Biased

unBiased

Example 3: In a survey of 800 people, 20% said they get a haircut once per month.

- What is the margin of error for the survey?
- Give an interval that is likely to contain the exact percent of all people who get a haircut once per month

Between 16.5% and 23.5%

You Try……

Convenience

- An electronics company wants to know which aspect of their MP3 player is the consumers’ favorite. Technicians are required to ask the question to all customers calling for technical support. Identify the type of sample described.

2. Tell whether the sample in Exercise 1 is biased or unbiased. Explain.

3. In a survey of 1100 home buyers, 90% said they used a real-estate agent to research home listings. What is the margin or error? Give an interval that is likely to contain the exact percent of all home buyers who used a real-estate agent to research home listings.

Biased

Between 87% and 93%

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