Databases Reference
In-Depth Information
object will correlate a little higher or lower with a specific group or during
a specific time of day or through a specific channel for a day and then will
correlate a little lower or higher on another day. In that way, randomness
indicates that the lack of correlation in an independent object will fluctu-
ate. In general, randomness will cause the correlation, be it positive, nega-
tive, or neutral, between two objects to fluctuate.
Conversely, fluctuations in correlation may not be randomness. Rather,
fluctuations in correlation may be the presence of multiple patterns over-
laid on each other. For most retail stores the two largest patterns are
period of the week (i.e., weekday and weekend) and period of the day (i.e.,
morning before the workday begins, daytime during school, after school
and before the workday ends, and after the workday ends). A wonderful
example of such an apparent fluctuation dates back to the days before
cable television and digital video recorders. A m unicipal water works
department noticed unusual fluctuations in their water pressure. After
significant investigation, they found the source of the fluctuation in water
pressure. When a popular sporting event or movie was broadcast on net-
work television, members of that city were delaying a trip to the bathroom
so they could see the end of the television show. The fluctuation appeared
first as a spike in water pressure as fewer citizens were consuming water
and then as a drop in water pressure as an usually large number of citizens
ran to the bathroom and flushed their toilets. Eventually, that water works
department came to rate the popularity of television shows by the drop in
water pressure that occurred at the conclusion of that television show. In
this example, two patterns overlap the normal consumption of water. The
first overlapping pattern is the tendency to wait until a television show is
over to go to the bathroom. The second overlapping pattern is the popular-
ity of the television show, which influences the number of citizens willing
to delay their trip to the bathroom. In this way, fluctuations in correlation
may not be randomness but rather may be the presence of multiple simul-
taneous patterns not yet discovered.
Randomness is not actionable. The goal of Market Basket Analysis is
to produce actionable information. Significant fluctuations in correlation
between two objects indicate a pattern of randomness that can be neither
leveraged nor avoided. If the enterprise cannot forecast the correlation
between two objects, then the enterprise is left to the whims of chance.
For this reason, randomness is an indicator of a future area of investiga-
tion. Only when the overlaying patterns of correlation are each identified
can they become actionable information for the enterprise.
