eBay bidders v. eBay sellers

I'll probably have more to say later about my eBay column (many thanks to the authors of the WSJ's Informed Reader blog-slash-column for bringing it some additional attention), but here's a fun fact I omitted for space. It's not a case of bidders or sellers being irrational per se, but rather of sellers outwitting themselves.

Among eBayers, it's commonly known that bidding peaks after work and/or dinner, on the East coast. Therefore, one might think that it would make sense to schedule your auction to end during that window. In fact, most eBay tips books tell you to do just that, the Wharton professor Uri Simonsohn discovered.

Yet if you look at the data, they show that so many sellers are following that advice that it actually becomes counterproductive to end your auction when the most people are bidding. It turns out that there's a serious oversupply of auctions during that time frame.

Better to schedule your auction for a time when there may be fewer bidders on hand -- but also many fewer auctions.

(NB: In the graph below, the times given are Pacific Standard Time, a nod to eBay's location in San Jose. Add three hours to shift the pattern to Boston time.)

The percentages on the left (the top figure is 12 per cent) refer to the proportion of eBay auctions ending at a given time. (Update, 6/15/07: Simonsohn emails to remind me that the numbers on the Y axis also refer to the proportion of bids at each time of day. That's sort of obvious, if you look at the chart, but I should have made it clear here. Also, he clarifies that this chart represents bids for DVD's specifically, not all bids. The rough trend may well hold for other goods, even most goods, but this data set is about DVD's. My apologies for the oversimplification.) The X axis begins at 12 a.m.

[Yes, yes, I know this graph is close to impossible to read on this scale, but if I blew it up any bigger it would slow down the blog and I'd face the wrath of the tech people.* Here's the deal: both auctions and bids begin to pick up speed at 3 a.m. PST, then rise steadily until the lines cross at around 3:30 p.m. PST. (They also touch briefly at 8 a.m.) During peak bidding/selling hours, the number of auctions ending climbs much faster and higher than the number of bidders. The lines intersect again, on a downward slope, at 10 p.m. PST. To this amateur, it looks as if the optimum time to end an auction might be between, say, 8 a.m. and 3 p.m. PST.]

*UPDATE: Here's a legible version of that graphic, for those who think graphs should be looked at, not read about.