Page 270 - Statistics for Dummies

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Part V: Statistical Studies and the Hunt for a Meaningful Relationship
The school district is proposing a 0.01% increase in sales tax to provide
funds for a new high school to be built in the district. What’s your opinion on
the proposed sales tax? (Possible responses: strongly in favor, in favor, neu-
tral, against, strongly against.)
If the purpose of a survey is purely to collect information rather than influ-
ence or persuade the respondent, the questions should be worded in a neu-
tral and informative way in order to minimize bias. The best way to assess
the neutrality of a question is to ask yourself whether you can tell how the
person wants you to respond. If the answer is yes, that question is a leading
question and can give misleading results.
If the results of a survey are important to you, ask the researcher for a copy
of the questions used on the survey so you can assess the quality of the ques-
tions. When conducting your own survey, have others check the questions to
verify that the wording is neutral and informative.
Selecting the sample
After the survey has been designed, the next step is to select people to partici-
pate in the survey. Because typically you don’t have time or money to conduct a
census (a survey of the entire target population), you need to select a subset of
the population, called a sample. How this sample is selected can make all the dif-
ference in terms of the accuracy and the quality of the results.

Three criteria are important in selecting a good sample, as you find out in the
following sections.

A good sample represents the target population
To represent the target population, the sample must be selected from the
target population, the whole target population, and nothing but the target
population. Suppose you want to find out how many hours of TV Americans
watch in a day, on average. Asking students in a dorm at a local university to
record their TV viewing habits isn’t going to cut it. Students represent only a
portion of the target population.

Unfortunately, many people who conduct surveys don’t take the time or
spend the money to select a representative sample of people to participate in
the study, and they end up with biased survey results. When presented with
survey results, find out how the sample was selected before examining the
results of the survey and see how well they match the target population.

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