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Sampling Methods and Bias in Population Surveys

Learn about different sampling methods such as self-selected, systematic, and convenience samples, and understand the concept of bias in population surveys.

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Sampling Methods and Bias in Population Surveys

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  1. Warm-Up • Use the normal curve on page 264 in your text to answer the following questions:

  2. Sampling methods

  3. A population is a group of people or objects that you want information about. A sample is a subset of the population. Population Sample

  4. There are multiple ways of sampling. • self-selected sample - members of a population can volunteer to be in the sample Ex: The reporter writes a column asking workers to call a special phone number and identify where they eat lunch during a typical work week. Reasoning: The workers can choose whether or not to respond. So, the sample is a self-selected sample

  5. systematic sample, a rule is used to select members of a population (such as selecting every other person.)

  6. convenience sample - easy-to-reach members of a population are selected (such as those in the first row.) Ex: Interviewing people at a shopping mall as they walk by Ex: A group of students in a high school do a study about teacher attitudes. They interview teachers at the school, a couple of teachers in the family and few others who are known to their parents.

  7. random sample, each member of a population has an equal chance of being selected Ex: Each student in the class is assigned a number. Then numbered pieces of cardboard are mixed up and drawn from a hat Ex: Names are put into a spreadsheet. Then in the corresponding column, random numbersare assigned using a random integer function on the calculator.

  8. Bias vs. Unbiased • unbiased sample is representative of the population you want information about. • biased sample a sample that overrepresents the population or underrepresents part of the population

  9. Bias or Unbiased?? BIASED • The reporter writes a column asking workers to call a special phone number and identify where they eat lunch during a typical work week The sample is biased because the sample is self-selected and it may not be representative of the population the reporter wants information about BIASED • A company wants to know how often it’s employees use the company’s cafeteria for lunch. The company asks employees who have just finished eating lunch on a Friday. The sample is biased because they are not sampling the employees who are not in the cafeteria.

  10. Biased or Unbiased?? UNBIASED • A gym is conducting a survey to find out how often members attend the gym each week. A gym employee asks every other person attending the gym how often they attend in a week. Work: Pg 269; 1-2 Pg 270; 1-3 Pg 271; 1-3

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