Which activity (correlation or regression analysis) is involved in each of the following situations?
a. Investigating to see whether there is any measurable connection between advertising expenditures and sales.
b. Developing a system to predict portfolio performance based on changes in a major stock market index.
c. Constructing a budgeting tool to express costs in terms of the number of items produced.
d. Examining data to see how strong the connection is between employee morale and productivity.