The owner of a chain of supermarkets notices that there is a positive correlation between the sales of beer and the sales of ice cream over the course of the previous year. Seasons when sales of beer were above average, sales of ice cream also tended to be above average. Likewise, during seasons when sales of beer were below average, sales of ice cream also tended to be below average. A plausible explanation of these facts is that:. a. the sales records must be in error. There should be no association between beer and ice cream sales.
b. drinking beer causes a desire for ice cream or eating ice cream causes a thirst for beer.
c. a scatter plot of monthly ice cream sales versus monthly beer sales would show that a straight line describes the pattern in the plot, but it would have to be a horizontal line.
d. the sale of beer and ice cream may both be affected by another variable such as the outside temperature.
e. none of the above.