
New research: cashiers who have their own lines move customers more quickly - qazmonk
http://www.scientificamerican.com/article/the-science-of-getting-through-a-checkout-line-faster/
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panic
Reading the paper ([http://whitman.syr.edu/faculty-and-
research/research/pdfs/BQ...](http://whitman.syr.edu/faculty-and-
research/research/pdfs/BQ_Rev2_MS_May5.pdf)), it looks like each customer took
the same amount of work to "check out" (moving five sliders to the correct
position). The whole reason to divide a single line across multiple cashiers
is to keep one slow customer from slowing down an entire line, so it's weird
they didn't model this in the experiment itself.

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cortesoft
Yeah, and also one of the keys gains is a lower deviation, which is a benefit
separate from faster average times.

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neild
This article fails to recognize the difference between throughput and latency.
A single queue optimizes for latency, since slow customers don't stall the
ones behind them. If cashiers work faster in a multiple queue setup, then this
configuration will optimize for throughput while still losing at latency.

As a customer, all you care about is latency: How long you spend waiting in
line. As a store owner, you also care about throughput: How many cashiers you
need to process some number of customers per unit time. A store owner that
cares about customer satisfaction will still care about latency, of course.

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ThrustVectoring
Higher throughput necessarily means lower average latency. Little's Law. What
the single queue helps with is reducing the variance of latency. That, and it
makes handling more involved interactions easier to do without inconveniencing
people waiting behind them.

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barrkel
Higher throughput does not imply lower average latency. Think pipelining with
lots of parallelism. Think of a system that makes everyone wait for ten
minutes then sends them to one of a million cashiers. Such a system would have
enormous throughput with very high latency.

Little's law doesn't imply what you said, either. It tells us the number of
people in the system based on arrival and wait, but nothing about throughput.

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ThrustVectoring
If the number of people in the system remains constant over time, then you can
measure throughput by counting the rate at which people either arrive or get
processed.

And you're right about throughput, I was implicitly holding the number of
people in the queue constant, and you can obviously add arbitrary delays and
increase the number of people in queue without touching throughput.

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jedberg
My thoughts on this:

Mathematically a single queue is far more efficient.

The psychology suggests that someone seeing a line makes them work faster.

First off, this is fleeting -- in a just a few years, we won't need people at
the registers anymore as RFID technology gets cheap and more people become
comfortable with the ever improving self checkout.

Secondly, even if you assume we will have checkers for a long time, this is
again an easy problem to solve. You have a single queue, and then you make
part of their pay based on average time per client or their evaluation.
They'll work faster because of it (maybe).

A counterpoint to my own point is that Target does rate their checkers on
efficiency, and I've watched them game it before. The checker meticulously
lined up all my items with the barcodes in a row, then hit the "new customer"
button, quickly scanned all the codes and hit the "total" button, giving him a
very fast time. He figured out that they only measure from when he says "new
customer" to total, so even though he was slower than everyone else, he had
the fastest time.

But my overall point is that humans will soon be out of this loop anyway.

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ScottBurson
> Mathematically a single queue is far more efficient.

No. In the absence of behavioral effects such as the ones suggested here, the
reason to have a single queue is not to reduce the _mean_ time for a customer
to check out, but to reduce the _variance_. With one queue per cashier, if you
happen to get behind the person paying entirely with pennies, you're screwed.
With a single queue, the additional latency introduced by such a customer will
be distributed among all the customers who aren't being served yet, rather
than just the few people behind them in the same queue.

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jedberg
But it's the variance that you want to reduce if you want to be more efficient
about resource usage (ie. cashiers and cash machines). As variance goes up,
your overhead for burst capacity goes up.

Also, variance is what people perceive as bad service, not the mean time. If
everyone takes a little longer they feel happier because of the perception of
fairness.

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SEJeff
Without reading the article, I've never seen anything remotely as efficient at
scale as Apple Store employees that all have handheld swipers. It scales out
linearly and is best because someone who is a tech can still double as a
checkout person. It also makes for a much more pleasant user experience IMO.

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CptJamesCook
I often can't stand the Apple Store model. I walk in to buy headphones and
stand around like an idiot waiting for one of the employees to be free to ring
me up. Just give me a line to wait in, please.

This problem has improved significantly in the past couple of years, I imagine
due to Angela Ahrendts takeover of the stores, but I still find it annoying.

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djrogers
Why wait? Just use the self checkout and get on your way...

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porFavor
How about studying the most 'human' checkout setup?

Used to be that you could make small talk and feel the hole in your pocket
growing bigger while you handed over that old crinkly dollar bill. Now I can
hardly get out a perfunctory "Hello, how are you doing?", because I'm too busy
trying to figure out whether I need to explicitly choose credit or whether I'm
going to need to sign or not given the dollar amount... I'm not suggesting
that we go back to the "good old days". I would, however, suggest that we
progress in the direction of pathos and our shared humanity rather than toward
whatever it is that tickles the fancy of Homo Economicus.

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keithpeter
Local produce market: open shout on prices - the most fun time to go is
between 3pm and 4pm when they are cutting prices (crossing off the old price
and writing the new one on the little cardboard placard stuck in the stock
display) or putting more produce in the '£1 per bowl' displays to clear stock.

Economics in action. Lots of people. You don't have to engage with the small
talk if you don't want to.

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JustUhThought
Sounds fun :)

I'm in Austin, TX. Looks like you in the UK. I'm going to look into whether
there is something like this locally. Thx!

Also, just curious. What are your thoughts on the EU vote coming up?

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keithpeter
_" Also, just curious. What are your thoughts on the EU vote coming up?"_

My thoughts?

1) Look at a map centred on 52N02W with a radius of 2000 miles and think about
what the future is for an island off the mainland with a population about two
and a half times that of Texas.

2) Daniel Kahneman would have a field day over here at the moment! A fair
spread of his hypotheses can be seen in action daily.

PS: I was describing Birmingham's central food markets in Digbeth by the way,
but other cities have good markets as well - open three or four days a week
and selling the same kind of stuff you can get in supermarkets without the
packaging. We also have more expensive/artisanal 'farmer's markets' with
higher priced produce in middle class areas, typically one Saturday a month.

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logicallee
I agree with the other posters here, this is a really bad article. Even if the
effect is true, it doesn't matter because nobody cares if you take 20 seconds
or 30 seconds to check out. I care about the fact that when cashiers had their
own lines, I had to stand for 5 minutes behind someone who tried to use a
points-based rewards card, didn't have quite enough on it, then the cashier
went through something complicated so she could deduce what he did have,
document and sign it, and have him pay the tiny cash difference between his
sum and what he had on his card. It literally took 5 minutes, while I was
trying to buy like milk and bananas or something. Of course, I thought about
the well-known research on single queue. When I saw other lines moving, I
wished I had been in one.

plus, this appears to be the result of an experimental setup rather than real-
world facts. It's trivial to get real-world data from some place that
implemented the difference, since _all_ receipts are time-stamped. You just
have to count the number of receipts in single-line, vs everyone-with-their-
own-line, and see which is bigger. (You can also see how average total or
number of items differs between setups, or normalize for any changes, such as
only considering the time taken to ring up literally the exact same order.)

this isn't data rocket science. any store which went single-line should have
this data.

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rileymat2
I am a bit suprised they studied this with lab experiment as opposed to
observations at a real store with professional cashiers.

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bunderbunder
It's a tricky one. You can't infer any sort of causality by just looking at
real stores, because the policy varies by store or chain. So there are a
zillionty (to be precise) other variables changing along with whether they use
a common queue or not. Any difference you see could be due to any of them. And
just taking an existing store and trying to randomize the policy is still
tricky, since the form of queue you use influences the physical layout of the
store and you might get weird effects from a mismatch.

But doing it in a lab means you have no ecological validity. People know
they're being watched closely, much more closely than they would be in a real
life scenario, and that will affect their behavior. So you really can't be
sure your results will generalize to the real world.

Possibly the best you can do is take a few stabs at both approaches and hope
that all the studies point in roughly the same direction.

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lostlogin
> there are a zillionty (to be precise) other variables.

I hit all of them every time I go. It's awful. The old person returning a head
of broccoli, the kid pulling down a display stand into my shopping on
conveyer, the milk bottle leaks onto cashier. Every time I go it's a new kind
of pain.

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aaron695
But it's a useless result.

As a customer I only, only care about my perception of speed, not actual
speed.

Multiple lines 'seem' fair, there's also little variance and hence I leave
feeling positive most of the time.

A store might save a small percent on cashers using this research but pissing
the customers off the huge amount it would seems like poor economics.

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ubernostrum
_As a customer I only, only care about my perception of speed, not actual
speed._

Which in turn can be gamed. See the infamous story from Houston, where there
were large numbers of airport complaints saying it took too long for arriving
baggage to reach the bag claim. The solution was:

[http://www.nytimes.com/2012/08/19/opinion/sunday/why-
waiting...](http://www.nytimes.com/2012/08/19/opinion/sunday/why-waiting-in-
line-is-torture.html)

(they rearranged things to increase the distance between arrival gates and bag
claim; it still took the same amount of time to deliver bags to bag claim, but
now passengers spent more time getting to the bag claim and less time waiting
_at_ bag claim, so they perceived it as faster and complained less)

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cbanek
I've also heard a similar story about complaining about elevators taking a
long time, but after installing floor to ceiling mirrors in the lobby, people
were distracted enough where it didn't feel like it took as long and stopped
complaining.

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mynegation
I am wondering if anyone put real-world details into mathematical models. In
case of a single line and multiple cashiers, people tend to stand farther from
the cashiers than they would be standing if they had chosen specific line and
it requires tiny bit of attention and delay to scan cashiers constantly.
Depending on the shop/service, if you choose the line you may start putting
out your purchases onto the conveyor belt while the person in front of you is
still being served, not so much when you do not know your cashier in advance.

From my airport experience, hybrid models tend to be pretty good: one single
line to security scan or passport check and then it is ushered into many short
ones. Probably should mathematically model that and see what happens.

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icebraining
One of the supermarkets around here has an automated alerting system that
tells the next person in line which cashier they should move to (they use a
large screen and a recorded voice).

The notification comes when the cashier moves to the payment step, so you
still have time to unload the purchases onto the belt before the previous
customer is finished.

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umanwizard
As a former McDonald's cashier/drive-thru operator, this makes intuitive sense
to me.

There is a very real stress you feel when a line starts building up. I
naturally worked harder when it felt like I was falling behind.

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e2e8
You are saying that when your individual line starts building up you feel
pressure but when the single global line starts building up you would not feel
pressure?

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hueving
Yes, a single global line build-up doesn't feel solely like your
responsibility. It's like a tragedy of the commons scenario.

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iam-TJ
Ode to the cashier.

    
    
      First they came for the waiting room, and I did not speak out -
      Because I did not mind to queue.
    
      Then they came for the stock pickers, and I did not speak out -
      Because I did not mind to pick.
    
      Then they came for the cashiers, and I did not speak out -
      Because I did not mind to be anti-social.
    
      Then they came for me - and there were only robots left to speak for me.

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abpavel
Mathematical model matches, since a mathimatical arbiter eliminating Head Of
Line blocking also incurrs the additional latency penalty due to the extended
path and additional switching elements. However the latency penalty is
incomparable to the improvement in latency variance.

I can't believe they've ommited a situation where this one lonely customer
answers "Yes, I DO want to hear more about the offer" and starts signing up
for the store membership, a bonus program, a store credit card, a cat
insurance, and a dunce hat.

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cbanek
I think there's also some real world components of one queue vs many queues
that are missing here.

For example, at a hotel checkin, flight baggage checking, or Fry's
electronics, there is one line which feeds into multiple agents. As the number
of agents grows, there's a nontrivial amount of time where an agent is done
with the current customer, but the next person in line has to walk maybe 50 or
so feet to them, wasting some time, especially if they are slow (kids,
luggage, elderly).

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dewiz
Maybe separate queues work better, but that creates competitiveness, and in a
long term will stress workers more, who might eventually slow down and feel
judged by others.

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dewiz
Does it mean that a team of developers where each developer is responsible for
a feature (vs the team being responsible for all features) will deliver
quicker?

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sandworm101
Simpsons s05e13

APU: "Look, Mrs. Simpson, the express line is the fastest line not always.
That old man up front, he is staved for attention, he will talk the cashier's
head off."

I think The Simpsons got it twenty years ago: when it comes to checkout lines,
the human factor means far more than the mathematics.

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turbostyler
That's great, but having one line per cashier is not spatially efficient.

