Suppose that you are an entrepreneur interested in establishing a new Internet-based sports information service. Furthermore, suppose that you have gathered basic demographic information on a large number of Internet users. Assume that these 1000 individuals were carefully selected through stratified sampling. These data are stored in the file P2_43.XLS. 

a. To assess potential interest in your proposed enterprise, you would like to conduct telephone interviews with a representative subset of the 1000 Internet users you surveyed previously. How would you proceed to stratify the given frame of 1000 individuals to choose 50 for telephone interviews? Explain your approach and implement it to select a useful sample of size 50. 

b. Explain how the entrepreneur could apply cluster sampling to obtain a sample of size 50 from this frame. What are the advantages and disadvantages of employing cluster sampling in this case?