Sampling Method. determine whether the sampling method appears to be sound or is flawed.
Text Messaging In a survey of 109 subjects, each was asked to indicate how many text messages they send and receive each day. The sample consisted of those who chose to respond to the request posted on the StatCrunch Web site.
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The sampling method is flawed.
The sampling method introduces the possibility of nonresponse because the sample did not count those subjects who did not choose to respond.
This nonresponse further leads to missing data as a result of some subjects never responding.OR
The sample is a voluntary response sample and is therefore flawed.