A Pew Internet poll in 2010 asked mobile phone users about how they used their mobile phones. One question asked...

A Pew Internet poll in 2010 asked mobile phone users about how they used their mobile phones. One question asked whether or not during the past 30 days they had used their phone while in a store to call a friend or family member for advice about a purchase they were considering. The poll surveyed 1005 adults living in the United States by telephone. Of these, 478 responded that they had used their phone while in a store within the last 30 days to call a friend or family member for advice about a purchase they were considering.

(a) Construct a 90% confidence interval for the proportion of U.S. adult mobile phone users who had used their phone while in a store within the last 30 days to call a friend or family member for advice about a purchase they were considering. [4 marks]

(b) In the previous survey in 2007, a poll reported this same proportion to be 55%. Using the data from this poll in 2010, test the claim that the proportion of U.S. adult mobile phone users who had used their phone while in a store within the last 30 days to call a friend or family member for advice about a purchase they were considering has declined since 2007. Use all steps for hypothesis testing to make a conclusion at a significance level of 10%. [6 marks]

(c) What assumptions or conditions have you made in statistical inference in parts (a) and (b)? Are they being satisfied? [3 marks]

Marking Criteria: You need to show all working. No marks awarded for the correct answer without working out. For full marks, you need to demonstrate understanding of the statistical inference concepts involved in each part of this question as well as an answer expressed in an English sentence.