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"One line to rule them all"?
Jane Galt writes:
Everyone knows the unified queue is the best way to move checkout traffic. So how come every time customers in a crowded drugstore try to form a single queue, the cashiers force us to line up at the registers? Do they get some kind of psychic job from knowing in advance which customer they'll check out?
You might try to argue that the indirect utility function is convex (risk-loving) in prices, and that people, when they realize that their personal line-choice algorithms result in shorter (longer) waits, make more (fewer) trips to the store. Samuelson once proved a theorem about that in the QJE. 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.
And might there be "line price discrimination"? Hurried people like me can scout out the best lines (don't you have visual algorithms for speedy cashiers?...young girls are best), whereas the conversation-starved, check-writing old ladies might even prefer a slower line.
There are thousands of papers on queuing theory, but I've never seen a good study of when single lines are to be preferred. How sad indeed is my profession...
Posted by Tyler Cowen on June 28, 2007 at 10:54 AM in Economics | Permalink
Comments
I do not know what drug store she goes to, but the ones I go to everyone forms a single line -- both at the main counter at the front and the prescription counter at the back of the store.
Posted by: spencer at Jun 28, 2007 11:32:56 AM
Did you see this a few days ago, about the unified line at Whole Foods in New York?
Posted by: nicole at Jun 28, 2007 11:35:35 AM
Multiple queues take up less floor space. (You don't need to leave space between the single queue and the checkers for shoppers to move to the open clerk.) Retailers are evaluated based on sales per square foot. Ergo, multiple queues.
Posted by: mkl at Jun 28, 2007 11:56:32 AM
As always, The Simpsons has already been here. From the episode when Apu lost his job at the Quick-E-Mart:
Apu: Let's go to...that line.
Marge: But that's the longest.
Apu: Yes, but look: all pathetic single men. Only cash, no chitchat.
Posted by: David J. Balan at Jun 28, 2007 12:01:29 PM
mki, I have never once been to a grocery store that had every checkout line staffed and open. Extra, unused lanes are all wasted floor area, from a revenue standpoint. A single queue may waste some space (though I don't think it has too) but would make more profitable use of manpower by allowing more efficient allocation of workers to check out duties because single queues have much less risk of server under-utilization. Maximizing profit per sq ft also fails to explain why some businesses (even retail businesses) do use single queues. Best Buy is notorious for scientific attempts to maximizing profit margins, but I've been in a few with single queues.
Posted by: Jared at Jun 28, 2007 12:08:19 PM
A single, zig-zag line does not waste any more floor space than multiple lines.
Posted by: Harish at Jun 28, 2007 12:15:12 PM
Is it really the case that young girls are fastest, or is there an element of Einsteinian relativity going on here? (Sit down with a pretty girl, and time just flies...)
Posted by: Ted at Jun 28, 2007 12:26:22 PM
The worst queues in our memories--airports, banks, the old DMV--are single-line.
Is it any wonder we prefer to try hub-and-spoke? (Not to mention to be able to select [or avoid] particular cashiers at places frequented often enough that pecadillos become known, positively or negatively.)
Posted by: Ken Houghton at Jun 28, 2007 12:51:13 PM
My theory is that there are multiple lines when every customer takes (within reason) a similar amount of time to get through, but there is one line when some customers might take much, much more time than others.
For instance, there are multiple lines at McDonald's. But for customs and immigration at the airport, there is one line. That way, if some suspicious-looking guy gets a thirty-minute interrogation, nobody has to wait half an hour behind him.
Banks, same thing. Some people have complicated banking transactions that take forever, and this way nobody has to wait for those people.
Posted by: Phil Birnbaum at Jun 28, 2007 12:54:37 PM
At the Commissary at Fort Bragg there was a single line that moved very quicly. That was combined with a telephone number you could call that would tell you the current waiting times (if they were too long, you might want to go another time). At Costco they bragg that a waiting line will never be more than three people long (if one is, they will get another cashier or other help). We rarely go to a chain restaurant (Outback, Chilis, etc.,) on a Friday or Saturday evening because the wait is too long, opting for less crowded restaurants or making reservations..
On the other hand, if you can wait in line and do something productive, waits may be good.
Opportunity cost is certainly something to take into consideration.
Posted by: Allan at Jun 28, 2007 12:56:44 PM
I'm glad someone has noticed the advantage of women grocery check-out clerks. Not necessarily the young ones. I think it's because there is still more "opportunity" for middling-competent men (often they're the one who have become managers and OK checks from the people they don't know but the checkers do) than for middle-aged women.
I'll go for a forty-ish gal any time. I think the "young" part is an "extra" courtesy of Tyler.
Posted by: who, me? at Jun 28, 2007 12:58:26 PM
[Similar to a comment I posted at AI]
Basically, anything that requires an agent to wait for a customer causes the average wait time to go up. Everyone has had to remind someone in front of them (at the airport, say) that the next agent is ready, and then the agent still might have to wait for a leisurely stroll over. In some scenarios, these costs can be very high, even infinite. How much more efficient would a taxi-line be if every time a taxi was ready there was someone standing next to it ready to get in? I think they get this right in Vegas, but definitely not in NYC.
I think the ideal in general, if you have the resources, is a hybrid system like the returning customs line at JFK -- a big single line feeding into short lines for each agent. This maximizes throughput while keeping variance low.
Posted by: fmb at Jun 28, 2007 1:11:51 PM
I think multiple lines is also advantageous in terms of pushing impulse items. A fast moving single line prevents one from picking up a gossip rag or a pack of gum.
just a thought
Posted by: TK at Jun 28, 2007 1:16:40 PM
"I think multiple lines is also advantageous in terms of pushing impulse items. A fast moving single line prevents one from picking up a gossip rag or a pack of gum."
Fry's Electronics (essentially a grocery store for electronics) has this down pat. The normally have 20-40 checkers, a single long serpentine line, and in the line has impulse purchase items all along it. It is a great place to shop for electronics if you know what you want, if anyone in town has it, they do. Just don't ask for advice on anything (that is why they are cheap).
Posted by: Sebastian Holsclaw at Jun 28, 2007 1:25:20 PM
I posted a similar item (more specifically about the Whole Foods example)on
Posted by: Jodi Beggs at Jun 28, 2007 1:34:15 PM
I posted a similar item (more specifically about the Whole Foods example)on my blog earlier in the week. There are a number of young economists that are specifically studying supermarkets,
and they have a lot to say on the topic...it's only a matter of time until they
get around to studying the lines leading up to the registers.
Posted by: Jodi Beggs at Jun 28, 2007 1:36:05 PM
I posted a similar item (more specifically about the Whole Foods example)on my blog earlier in the week. There are a number of young economists that are specifically studying supermarkets,
and they have a lot to say on the topic...it's only a matter of time until they
get around to studying the lines leading up to the registers.
Posted by: Jodi Beggs at Jun 28, 2007 1:37:46 PM
We rarely go to a chain restaurant (Outback, Chilis, etc.,) on a Friday or Saturday evening because the wait is too long, opting for less crowded restaurants or making reservations.
I've noticed that chain restaurants tend to (slightly) overestimate the waiting times during busy periods. If the hostess at, say, Outback says that the wait is 35 to 40 minutes, it's more likely to be 30 to 35 minutes.
Posted by: Peter at Jun 28, 2007 1:43:04 PM
Well... I had a teacher in one of my principles of economics classes relate this one, he always said it didn't matter which lane you chose, your average expected waiting time would be the same, and this was according to the efficient markets hypothesis. I always think about that when looking for parking spaces or waiting in grocery lines, or even driving on the freeway.
Incidentally, I've been to several stores that have single-line queues. Marshall's most recently. It seems pretty efficient and fair in that setting. Single-line queues wouldn't work in grocery stores because of item count disparity. It enables grocery stores to capture additional small-item sales by reducing the opportunity cost to less numerous item purchasers.
Posted by: Nathan at Jun 28, 2007 2:54:21 PM
I'd rather them overestimate than under estimate.
Posted by: Robert S. Porter at Jun 28, 2007 3:03:45 PM
See a discussion on the single-line problem (and related design issues) here.
Posted by: Peter G. Klein at Jun 28, 2007 3:10:15 PM
Has anyone heard the theory that lines form according to a bell curve (where the busiest lanes in a supermarket are the middle ones and the lines are shorter towards the end)? I heard this when I was a kid, but I never believed it.
Posted by: Klug at Jun 28, 2007 3:23:42 PM
It seems like a single long line would be less efficient, since it takes time for customers to go from the single line to a particular cashier, and the cashier will not be doing anything during that time. This is especially true in grocery stories, where many customers have a cart to unload, but it is also true to a lesser extent in places like drug stores. If there is one line per cashier, and customers easily outnumber cashiers, then each cashier will be working pretty much constantly, since there will almost always be another customer in place for the cashier to deal with (with some of their purchases waiting on the counter) as soon as one customer is finished. A single long line would be more equitable (less variability in waiting time) but less efficient (higher average waiting time).
Posted by: Blar at Jun 28, 2007 4:07:55 PM
Further to spencer's point, at the drug stores I go to, people form more of an amorphous blob than a single or multiple line. Everyone kind of knows that they're in one of the lines, but they also kind of watch out for everyone else, and act kindly if they notice that someone has been waiting for a long time at "the wrong register." It kind of turns into one of those days where you're at the butcher counter and the "pick a number" machine is broken.
Further to Ken Houghton, it's definitely more traumatic to be in a single line. The only time it's less traumatic is when we see a person who is actively monitoring the line and moving people quickly to the next available register. I think multiple lines give people a sense of control, relative to the herd of single lines. Having a store employee manage the line can restore consumers' confidence greatly.
Further to Klug, I think the better rule would be that lines form according to how the store is laid out. My regular supermarket is laid out so that shoppers always exit the store on the side of the building where register #1 is, so inevitably #1 is the most full and #20 is the least full. A single line would be upsetting to me in this situation, because I am a frequent shopper, and I know the farther registers are always most efficient -- sometimes you can actually see check-out clerks waiting idle at a far register while they are very busy at a near one -- so I would in fact lose out if my grocery store switched to this system.
BTW my supermarket has lower ceilings than most grocery stores and department stores, (I gather that it holds culinary classes and whatnot on the second floor,) so it's actually slightly more difficult to see across the room to register #20 unless one looks more carefully. Also, I have found that when an employee of this supermarket tries to guide me to the next best available line, they are almost invariably WRONG. I ignore them. The only ones I listen to are the ones where the checkout person actually leaves their register and comes to collect me personally, saying "I'm open on 18."
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