Thursday, April 28, 2005

Amazonian Higher Mathematics

Once in a while I get an e-mail from Amazon.com, entitled "Amazon Recommends," which lists books, music, and movies that I might like, based on my one-to-five-star ratings at their website (a fine way to pass the time if you're suffering from headache, or putting off doing things you really ought to have done last week), or based on past purchases. Many of these recommendations are quite good, although I doubt I've ever made an Amazon purchase on the basis of one. Many are bad. That is to be expected, though making me snort haughtily is probably not the reaction the Amazonians anticipated. Some are completely out to lunch (such as recommending Robbe-Grillet on the basis of my liking for Trollope.) And most are merely indifferent -- plausible, but not compelling.

Recently, they've added a mathematical twist, presumably based on probability theory, although the basis of the calculation is quite mysterious -- and the outcome so dull, and so ambiguous in its implications, as to still any lingering mathematical curiosity concerning exactly which procedures might result in the (highly specific) outcome. If what it all means is open to doubt, what it all means to me is doubly so. (Actually, 2.14297735ly so, but I'm rounding.) If I'm X times more likely to buy A than other Amazon customers (whatever that means), what am I expected to make of that fact? Indeed, it seems to me (a certifed contrarian) that knowing I was Y times less likely to buy A than other Amazon customers would carry more weight.

In any case I've appended here two examples from Amazon's most recent helpful letter. Any interesting mathematical or psychological insight into this phenomenon (no matter how implausible) would be appreciated.

Herewith, then:

We recommend The Long Goodbye (Vintage Crime/Black Lizard)
http://www.amazon.com/o/ASIN/0394757688/ref=pe_arr_d_0394757688_5_txt List Price : $13.00 Price : $10.40 You Save : $2.60 (20%)Because you purchased or rated: * Farewell, My Lovely (Vintage Crime/Black Lizard) You are 13,759 times more likely to purchase this item than other customers. We recommend Suspended Night http://www.amazon.com/o/ASIN/B0000V765G/ref=pe_arr_d_B0000V765G_6_txt List Price : $17.98 Price : $13.99 You Save : $3.99 (22%)Because you purchased or rated: * Storyteller You are 6,256 times more likely to purchase this item than other customers.