Page 202 - Algebra 1

INVES3TIGATION
Analyzing the Effects of Bias in Sampling,
Surveys, and Bar Graphs
To gather complete and accurate information about a particular population, researchers need to collect data from all of the population’s members.
Sampling It is not always practical to survey every individual in the population, so researchers use data from the sample to draw conclusions about the entire population. The table below identifies five sampling methods.
Sampling Method
Example
Simple Random
Select a group at random from the larger population.
Draw names of people to survey from a hat.
Stratified Random
Separate a population into smaller groups that have a certain characteristic. Then survey at random within each group.
Separate a herd of cows by breed; then survey a random sample from each breed.
Systematic Random
After calculating
the required sample size, survey every nth member.
Choose the number 5 at random. Survey every 5th person.
Convenience
Select individuals from the population based on easy availability and/or accessibility.
Survey the first five people who arrive at a local mall.
Voluntary
Sample individuals who self-select into a survey by responding to a general appeal.
A news program asks viewers to participate in an online poll.
Math Language
A population is a group that someone is gathering information about.
A sample is part of a population.
A sample is random if every member of the population has an equal chance of being chosen.
Online Connection www.SaxonMathResources.com
LuggageSurvey Aluggagecompanywantstoknowthemostpopular backpack color among high school students. Company representatives record the color of backpacks carried by boys in the cafeteria during lunch. Since the survey excludes high school girls, the sample is biased. It does not include some members of the population.
Analyze Give a reason why the sampling method may be biased.
1. A chef asks the first four customers who order the new cheese sauce if
they like it.
2. At a convention of science teachers, attendees are asked to identify what their favorite subject was in high school.
3. A librarian sends questionnaires about library usage to families with children.
Investigation 3 187