[This post was originally published on The Living Room Tumblr.]
Last week, inspired by a Planet Money podcast episode in which the “wisdom of crowds” was tested by having 17,205 people guess the weight of a cow based on a photo on the Internet, I decided to tweet out my wife’s picture of her giant Costco shopping cart and ask the Internet the same question my wife, Becky, had asked me: Guess how much this cost!
In the spirit of @planetmoney’s “wisdom of crowds” podcast, anyone care to guess how much this Costco haul cost us? pic.twitter.com/jRK5AQgKXS
— Brendan Loy (@brendanloy) August 17, 2015
The tweet was RT’d by @planetmoney, and the experiment took off. Well, okay, it didn’t “take off” in the “17,205 guesses” sense, but I got a decent response nonetheless: 43 guesses on Twitter, and, after I posted it on Facebook, 36 guesses there (excluding the 4 guesses that came after Becky gave it away – and also excluding the various “$1, Bob” joke-guesses, on both FB and Twitter). So, 79 guesses in all.
And they were almost all badly wrong.
The average guess was $404.15. The median was $356.72.
The actual price of the pictured Costco haul? $881.37!
That’s more than twice the average guess, and almost two-and-a-half times the median!
And no, there wasn’t a hidden diamond ring, fancy watch, insurance policy or coffin skewing the sample. The cart contained 86 items, at an average price of $10.24 per item. The most expensive item was the ream of paper, visible in the photo, at $29.99. (David Roberts was right about that, yet still off by more than $350 on the total.)
Facebook did better than Twitter at guessing the cost of the haul, though still with a fairly abysmal bottom line. The FB average was $444.56 (just over half the actual total), versus $370.31 on Twitter. That’s probably due to some combination of the “Stapleton factor” – quite a few of our FB friends are fellow residents of our kid-friendly neighborhood in Denver, many with multiple kids of their own, and thus a familiarity with the type of bulk shopping we do at Costco – and the additional bit of information that I gave in the my Facebook post, hoping to counteract the misconceptions that I thought were helping to fuel the way-too-low guesses on Twitter:
But even on Facebook, almost nobody was close. Katie Poch came the closest, guessing $847.36 (off by just 4%). The next closest was Kristy McCray, at $785, followed by Ed Maa at $723. Everybody else was below $700.
On Twitter, meanwhile, every single guess was below $600 – with one exception. The one & only person, on either social media platform, who “overbid” was @codethug, who guessed $1,200 (off by 36%).
Here’s a scatter chart:
Why did the crowd get this one so wrong, after guessing that cow within 5% of its actual weight? I’m honestly not sure. Obviously, the much smaller sample size is one explanation, though I’d find it more convincing if the 79 people who did guess hadn’t been almost literally unanimous in hugely underestimating the total. Even with a relatively small sample size, 78 out of 79 can’t be plausibly explained by random chance alone! Another explanation is that Becky’s photo didn’t provide enough information, by not showing the other side of the cart. But people surely knew there were unseen items, and calibrated their guesses accordingly – indeed, several said so – yet they were still way off.
The biggest issue seemed to be underestimating the number of items (86), rather than their average price ($10.24), which was actually lower than some guessed. I think, in large part, people may have simply failed to realize how resourceful Becky can be at sticking small items into tiny spaces between larger items in a giant Costco cart. 🙂 Many non-Costco shoppers may not have grasped how wide these giant Home Depot-style flatbed cart/trucks are. There are something like ~30 items visible in the photo, which would suggest a total of ~60 items if you assume a similar number on the other side. Yet in fact, there are almost 90 items. The cart is wide enough that there’s basically an entire middle layer of items in between the left side and the right side.
Anyway, just in case anyone doesn’t believe me about the total, here’s a scan of the receipt. And, for those wondering: we shop at Costco roughly every other month. This was an unusually expensive trip (hence Becky sending me the photo in the first place), but it always costs a lot. On the bright side, though, we barely spend anything on groceries or household essentials in our “off” month! Heh.
Incidentally, when Becky asked me to guess, via text message when she first sent the photo, I said $835. So there. 🙂
