June 28, 2007

Line-choosing algorithms

Posted by Arcane Gazebo at June 28, 2007 2:33 PM

Here's Tyler Cowen on why supermarkets seem to prefer individual lines at each checkout stand rather than one unified line (apparently Whole Foods uses the latter strategy).

The intuition is that consumers can take advantage of price variability, in this case "time price" variability, and come out ahead. Admittedly the notion of "going to the store more often when your innate line-choosing algorithm turns out to be good" requires a mental stretch.

People also might like knowing that the end to waiting is in sight. On the phone they put you on hold and tell you the expected wait time, or they should. At least five times in my life I've bolted a supermarket and abandoned the groceries, simply because the lines appeared too long. It is harder to estimate how long a single line will take, and it is harder to compare single lines across supermarkets.

I think there's something to this; seeing the long line stretching across the store can be daunting even though it may be moving quickly. I would also guess that multiple lines are more space-efficient. My local Safeway wouldn't have anywhere to put a unified line, and at busy times the individual lines fill the space at the front of the store as it is.

Actually, egregious lines are fairly common at that particular store during the evening rush, but luckily it's across the street from me so I can easily bail when it's too crowded and come back later. This strategy only works if I don't procrastinate my grocery shopping until it's urgent, but luckily the more upscale Andronico's is only one block further away and never has significant lines at the checkout, so I have a fallback. I hate waiting in line enough that I'll walk down to the next store to avoid it even if I don't save any time that way—at least by walking I get a little exercise and fresh air.

It might be better if I had a good innate line-choosing algorithm, but somehow mine is terrible—I suspect it's worse than chance, and that I would do better by throwing out my initial guess and choosing randomly from the remaining lines. But surely the readers here can help me improve it. How can I identify the fastest lines at the grocery store?

Tags: Life

Avoid any lines with children or older women (who tend to write checks). Find the line that has a pretty girl at the end and chat her up- it may not move any faster but you'll care less, plus you'll get a chance to practice your small talk and social skills. (Not that I would EVER do this myself, of course, but it seems a good strategy for a single guy.)

Posted by: JSpur | June 28, 2007 2:53 PM

I just go to the closest line to where I am in many cases because in many places, my view is blocked so I can't even see how long the various lines are.

By the way, as for supermarkets' choices, I'm pretty sure some of them have hired consultants who know appropriate things ("queuing theory" is the relevant subfield of probability, and single lines versus multiple lines is among the topics that have been studied extensively). Operations research (aka, industrial engineering) folks tend to be the ones who are hired for that sort of stuff.

Posted by: Mason | June 28, 2007 4:24 PM

Look for lines containing young-ish men shopping alone. They're likely to have fewer items, and more likely to pay with cash or a credit card. Women and couples are more likely to bust out the checkbook, and balance it at the register while you wait.

Posted by: Chad Orzel | June 28, 2007 5:15 PM

The single guys are also more likely to smell bad.

Posted by: Mason | June 28, 2007 5:21 PM

First, foremost, and most frequently overlooked: know your tellers. If you go to the same grocer regularly, you should pay attention to which ones are fast/efficient.

Other points:

  • Remember to approximate number of (scanned) items, not total bulk of groceries.
  • The granny with 20 coupons is going to take longer.
  • Avoid "floaters" -- some people try to solve this problem by ambiguously waiting between two lines (some more obnoxiously than others).
  • Learn to recognize (more general) douchebag customers. Probably the hardest thing to do.
  • Groups of people (families) standing at the checkout together tend to increase the perceived size of the line, making for easy pickings, so long as they're not too chatty (and, as a result, potentially sluggish to pay).

Posted by: Lemming | June 28, 2007 5:35 PM

I pretty much choose the number of items approximation and go to the line with the fewest item count (by rough approximation). The only exception for me usually is that I will check to see if the person currently being checked out is taking a long time/has a problem that is taking a while, etc. I've seen some lines that are really short count-wise, but it's because the person up front is having an argument, etc, so it's best to avoid that.

Posted by: Zifnab | June 28, 2007 9:17 PM

Avoid any line where the following sign is posted; "TSA training exercise in progress."

Posted by: JSpur | June 29, 2007 3:22 AM

self check out. or better yet a store near me has on cart computers check out as you shop.

Posted by: shellock | June 29, 2007 4:37 AM

I'm with Zifnab - in general look for low item counts. Of course, that sometimes bites me in the butt at Costco, because invariably one of those low item count people are buying something that needs to be retrieved from their secure area.

Oh, also watch out for check writers - they will always take longer.

Posted by: Chris L-S | June 29, 2007 7:54 AM

Costco you cant win. Last time i was ther i was in a fast line until rigth beofer me the did a teller swap. Had to wait 5 minutes for them to count and recount the till and puch out one person and in the next.

Posted by: shellock | June 29, 2007 8:44 AM

Thanks everyone, lots of good strategies for me to try. I've had limited success based on item count; since I always go to the same store at roughly the same time of day, I will probably do well by figuring out which cashiers are fastest.

JSpur: "it may not move any faster but you'll care less" sounds like something Tyler Cowen might say as well. However, the danger is that a failed effort will result in an even more agonizing wait as we stand around awkwardly.

Shellock: Neither of the two closest grocery stores have self-checkout, although I've used it at Albertson's when I lived in El Cerrito. My conclusion was that a fast express line is almost always faster than self-checkout; the clerk can scan items much faster than I can.

Posted by: Arcane Gazebo | June 29, 2007 1:53 PM

Just tried the item count approach at the Tom Thumb. Stood behind a woman who had three items. $4.18 total. For which she wrote a check. Then stood there complaining she couldn't find this, that and the other thing.

What's more she was fat. And ugly.

Maybe the answer is to order one's groceries online.

Posted by: JSpur | June 30, 2007 12:41 PM

Wow, you actually managed to use the self check out at Albertson's! I'm impressed. I've tried twice, once with two bottles of water (for a hike) and once with some carrots and some onion. In each case I quickly got into an infinite loop with the machine having me bag my first item, then insisting I remove it from the bag and recheck it. Each time I asked for help and my helper at Albertson's was unable to figure out how to end the loop, or having clearing the transaction, how to avoid it. Both times, my helper, and I've had two different helpers now, gave up, opened up an unused register and checked me out by hand!

Posted by: Kaleberg | June 30, 2007 7:14 PM
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