As you have seen in this resource, it is not always possible to survey every member of a group in order to determine the attitudes or beliefs of the members of the group. Therefore, it is important to select a sample of the population for the survey that is:
It is also important that the survey be asked in such a way that the questions do not skew the results of the survey one way or the other. Bias in a survey can influence the validity of the conclusions that can be drawn from the survey data.
For example, suppose that three students want to know which teacher is the favorite among all students at Lakeview Junior High School.
| Sandra surveys 120 students randomly selected using their student ID numbers. She concludes that Mr. Martinez is the favorite teacher at Lakeview Junior High School. | Hunter surveys 35 of his classmates in 7th grade, and determines that Mrs. Stephenson is the favorite teacher at Lakeview Junior High School. | Lakeshia surveys every third student in line at C lunch, and determines that Ms. Nguyen is the favorite teacher at Lakeview Junior High School. |
Sandra’s conclusion is valid because her sample is representative of all students at Lakeview Junior High School (every student had an equal chance of being selected for the sample).
Hunter's conclusion may not be valid because he only surveyed 7th grade students, and he wanted to determine the favorite teacher of all the students.
Lakeshia’s conclusion may not be valid because she only surveyed students at C lunch, so not every student in the school had an equal chance of being selected.