1.1. An online magazine which offers both free and paid for content has a large number of readers.  Readers can view additional content by paying a monthly subscription fee.  Based on reviews on the magazine’s website, the editor of the magazine believes that an additional type of content could be introduced.  Before making any changes, the editor decides to carry out a sample survey to obtain the opinions of the readers. 

Define the population that would be associated with the magazine.

1.2. Give one advantage and one disadvantage that would have resulted from the editor using a census rather than a sample survey.

1.3. The editor decides to gather opinions from only those readers who subscribe to the additional content.  A random sample of 25 subscribers is selected for the sample survey.

State two sources of uncertainty that may arise based on the chosen sampling method and sample size.