6.11 Nonresponse in a survey. In earlier versions of the Sallie Mae survey of Example 6.4 (page 350), participants were asked to report the undergraduate’s outstanding credit card balance. Only about a third reported this amount. Provide a couple of reasons why a survey respondent might not provide an amount. Based on these reasons, do you think the sample mean using just the reported amounts is biased? Is the margin of error based just on the reported amounts a good measure of precision? Explain your answers.