Lesson 11.4 Collecting Data Essential Question: How do you identify populations and sampling methods?

Before we start… Have you ever conducted or been part of a survey? Let’s survey the class… “What is your favorite sport?” “Don’t you think that watching a football game is more exciting than watching a tennis match?”

What is a survey? The entire group you want information about is called a population. Sometimes you survey a sample, which is a part of the population. A study of one or more characteristics of a group. A census is a survey of the entire population.

What are the sampling methods? Random sample Convenience sample Self-selected sample Systematic sample Stratified random sample

What is a random sample? Every member of the population has an equal chance of being selected.

What is a stratified random sample? The population is divided into distinct groups. Members are selected at random from each group.

What is a systematic sample? A rule is used to select the members of the population.

What is a convenience sample? Only members of the population who are easily accessible are selected.

What is a self-selected sample? Members of the population select themselves by volunteering.

How do you identify… Populations? Sample methods? Look for all members of a group affected by a survey. Who is being surveyed? Sample methods? The representation of the selected population. How were they selected?

Newspaper A school newspaper reporter asks every fifth student entering a school building whether a new gymnasium should be built. Identify the population and classify the sampling method.

Phone Survey A manager at a television station randomly telephones 75 residents under 30 years old and 75 residents 30 years old and over to determine the station’s most watched programs. Identify the population and classify the sampling method.

Employee Safety The owners of a company with several factories conduct a survey to determine whether employees are informed about safety regulations. At each factory, 50 employees are chosen at random to complete the survey. Identify the population and classify the sampling method.

Computer Games Owners of a computer store survey customers to see whether they should expand their game selection. They survey customers in the game aisle. Identify the population and classify the sampling method.

Restaurant Service A restaurant manager wants to evaluate the restaurant’s quality of service. Diners are given mail-in comment cards. Identify the population and the sampling method.

Extracurricular Activities Your school wants to know if students are satisfied with the school’s extracurricular activities. In each grade, every tenth student on an alphabetized list is surveyed. Identify the population and the sampling method.

Customer Satisfaction An airline wants to gather information on passenger satisfaction during a flight. A computer randomly selects 30 passengers to complete a survey. Identify the population and sampling method.

over-represented What is a biased sample? A sample that is not representative of the population. over-represented under-represented

Employee Safety The owners of a company with several factories conduct a survey to determine whether employees are informed about safety regulations. Suppose 50 employees are chosen at random from one factory to complete the survey. Is the method likely to result in a biased sample?

Computer Games Owners of a computer store survey customers to see whether they should expand their game selection. They survey all customers in the store on a Saturday. Is the method likely to result in a biased sample?

Neighborhood Watch A family wants to gather information from other residents on their street about forming a neighborhood watch. They survey every third house on both sides of the street. Is the method likely to result in a biased sample?

What is a biased question? A question that encourages a particular response. Survey questions should be worded to avoid bias.

Is the question biased? Why? Rewrite any biased questions. Don’t you agree that the voting age should be lowered to 16 because many 16-year-olds are responsible and informed?

Is the question biased? Why? Rewrite any biased questions. Do you think the city should risk an increase in pollution by allowing expansion of the Northern Industrial Park?

Is the question biased? Why? Rewrite any biased questions. Do you support the incumbent’s tax plan or the challenger’s tax plan?

Is the question biased? Why? Rewrite any biased questions. Don’t you agree that planting more shade trees will make our beautiful downtown area even better?

Is the question biased? Why? Rewrite any biased questions. Are you willing to pay higher taxes so that the city can build a new stadium, even though we already have a stadium?

How do you identify populations and sampling methods?

Ticket Out the Door Scientists wanted to gather information about the birds in a particular region. They chose observation sites and asked bird watchers at those sites to record the number and types of birds they saw in 3 minutes. What population was being studied?