WHAT DO YOU DO WHEN YOU DON’T KNOW WHERE TO START? WHEN YOU ARE DEALING WITH A DATA SET THAT offers no structure that would suggest an angle of attack?
For example, I remember looking through a company’s contracts with its suppliers for a certain consumable. These contracts all differed in regards to the supplier, the number of units ordered, the duration of the contract and the lead time, the destination location that the items were supposed to be shipped to, the actual shipping date, and the procurement agent that had authorized the contract—and, of course, the unit price. What I tried to figure out was which of these quantities had the greatest influence on the unit price.
This kind of problem can be very difficult: there are so many different variables, none of which seems, at first glance, to be predominant. Furthermore, I have no assurance that the variables are all independent; many of them may be expressing related information. (In this case, the supplier and the shipping destination may be related, since suppliers are chosen to be near the place where the items are required.)
Because all variables arise on more or less equal footing, we can’t identify a few as the obvious “control” or independent variables and then track the behavior of all the other variables in response to these independent variables. We can try to look at all possible pairings—for example, using graphical techniques such as scatter-plot ...