You see, I love math and numbers and graphs, and I have been collecting and reviewing those Diamond Sales Estimate reports for YEARS. For FUN. I'm telling you - I'm a total NERD.
I've noticed a simple pattern in the sales orders for titles after their debut. I think this is pretty commonly known. The #1 issue sales (the debut) will be its highest value, then subsequent issue #'s orders cool off rapidly until settling softly into a steady-state value. Like a cup of hot water cooling to room temperature. Some titles start much hotter others, and some titles cool faster than others, but the overall trend actually follows Newton's Law of Cooling pretty well. I've done least-squares regressions of the data and it's true (I know, I know... NERD ALERT!).
Here's the general pattern (CAUTION: ballpark percentages ONLY!!):
•By around issue #4-5, the sales have cooled to about 60% of #1 sales.
•By around the end of the first year, the sales have settled to about 40% of #1 sales.
Again, these percentages will be a bit different for the different books, but the OVERALL trends are pretty comparable. I have some graphs that make this point visually in a moment (!! NERD ALERT !!).
But first, here are two examples from many that show this cooling pattern in action (as .doc files):
John's XOMBI Sales Chart
2009 BATMAN & ROBIN Sales Chart
As you can see, the pattern is generally followed, regardless of how "cold" or how "hot" #1 sales are.