In a Previous Incarnation, I Was the Shell Answer Man

Natalie R. Collins has written a novel, Wives and Sisters, which sounds like equal parts suspense thriller and payback for being raised by and/or around sanctimonious Mormons...the latter, apparently, the primary subject of her ongoing blog. In recent posts, she's been tracking her Amazon ranking in comparison to that enjoyed by The Book of Mormon, and wonders aloud why her ranking slipped over 100,000 points in four days, while the Book only dropped by about 20,000.

As somebody who vaguely remembers the technical explanation I was given by my then-superiors when the sales ranking feature was instituted, I can explain it to her (and, by extension, you). This may be a little off, but I'll give it my best shot: the first 100,000 or so books are determined by the frequency of sales over the previous 168 hours, calculated hourly; from 100,001 to some other number is then determined by the frequency of sales over something like the last month... So, basically, if you sell even a dozen or so books within a very tight timeframe, it can create a momentary spike that will diminish exponentially as that block of purchases recedes into the past. On the other hand, if you're able to maintain a trickle of sales over a lengthy period of time, a dip in the daily sales will result in a comparatively smaller decrease in ranking.

It's not surprising, then, that a perennial like Book would have a ranking that doesn't fluctuate too sharply when viewed in relation to Amazon's total "inventory," while the positions for a novel like Collins' can veer almost erratically. The next questions worth asking are: what happened in the world that made enough people want to buy this book at nearly the same time? And can that event be duplicated? (And how?)