Database Reference
In-Depth Information
Chapter 1. Time Series Data: Why
Collect It?
“Collect your data as if your life depends on it!”
This bold admonition may seem like a quote from an overzealous project manager who holds
extreme views on work ethic, but in fact, sometimes your life
does
depend on how you col-
lect your data. Time series data provides many such serious examples. But let's begin with
something less life threatening, such as: where would you like to spend your vacation?
Suppose you've been living in Seattle, Washington for two years. You've enjoyed a lovely
summer, but as the season moves into October, you are not looking forward to what you ex-
pect will once again be a gray, chilly, and wet winter. As a break, you decide to treat yourself
to a short holiday in December to go someplace warm and sunny. Now begins the search for
a good destination.
You want sunshine on your holiday, so you start by seeking out reports for rainfall in poten-
tial vacation places. Reasoning that an average of many measurements will provide a more
accurate report than just checking what is happening at the moment, you compare the yearly
rainfall average for the Caribbean country of Costa Rica (about 77 inches or 196 cm) with
that of the South American coastal city of Rio de Janeiro, Brazil (46 inches or 117cm). See-
ing that Costa Rica gets almost twice as much rain per year on average than Rio de Janeiro,
you choose the Brazilian city for your December trip and end up slightly disappointed when
it rains all four days of your holiday.
The probability of choosing a sunny destination for December might have been better if you
had looked at rainfall measurements recorded with the time at which they were made
throughout the year rather than just an annual average. A pattern of rainfall would be re-
vealed, as shown in
Figure 1-1
. With this time series style of data collection, you could have
easily seen that in December you were far more likely to have a sunny holiday in Costa Rica
than in Rio, though that would certainly not have been true for a September trip.
