STAT 100 Lecture Notes - Lecture 1: Response Bias, Confidence Interval, Beta-Carotene
15 Jun 2018
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Assignment # 1 – Solutions
1.
a. Those people who do not take transit are clearly undercovered. The
surveyors have liberty to choose who they approach so their will likely be
some selection bias. The phrasing `eventually they get answers from 900’
suggests a serious problem with non-response but we are not give enough
information to judge how serious. (2 marks)
b. I expect there is response bias since the interviewers work for the company
the questions are being asked about. Moreover the coupling of
environmentally friendly with efficient means a respondent cannot say yes to
one and no to the other. You might think it environmentally friendly but
inefficient because it is so slow. This too generates response bias. (2 marks)
c. The quick method MOE is 1/sqrt(900) =1/30 =100/30 percent =3.3
percentage points. The estimated percentage is 100 x 720/900 = 80%. The
95% confidence interval runs from 80% -3.3% to 80% + 3.3% or 76.7% to
83.3%. (4 marks)
d. Definitely not. It summarizes ONLY the likely sizes of random variation due
to sampling. It does nothing about all the other types of errors listed in a and
b above. (2 marks)
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