Let them check you out
A couple years ago for a college assignment, I spent about an hour loitering in the soup aisle of a grocery store with two classmates and a stopwatch, for science. It changed my life forever (well, just a little bit).
If you ask people why they choose to use the self-checkout machine, they'll give you two reasons:
- I gotta go fast, and/or
- I hate interacting with people
Based on what we saw in these self-checkout (n=11) and human cashier (n=13) transactions, it's practically guaranteed that one of these is false, and the other doesn't have great odds either.
Speed
There are essentially four parts of any grocery store checkout, whether it's staffed robotically or with a human cashier:
- Waiting in line
- Scanning items
- Bagging items
- Paying for the purchase
Paying for the purchase is basically a wash - if you're using a credit card, this usually takes about 30 seconds for both cashier and self-checkout, including printing a receipt.
Waiting in line usually favors the self-checkout. In this supermarket and many others, a single queue feeds into four different self-checkout machines. This means that the self-checkout rate is quadrupled, and it also improves the variance: even if one person is being unusually slow (like when one customer tried to pay with a personal check, which took almost eight minutes to sort out), the line continues to move through the other three machines. [footnote 1]
Scanning and bagging items is the real time-sink, which also scales proportionally to the number of items you have. How fast do you think you can scan and bag an item at a self-checkout, compared to a cashier? 10% faster? 20% faster? The average customer we observed was about four times slower per-item than the average cashier. The absolute fastest of the customers, who seemed like a solid candidate for the barcode scanner Olympics, just about the same as the average cashier. It's almost as if cashiers scan a lot of items, and they're paid to do it for several hours a day.
The two "P"s, which is a term I just made up for Produce and Pipelining, also make the cashier much faster. If you have any amount of produce, you'll have tap through several self-checkout menus to select your item, while the cashier will often just tap in the item number from memory or look at a paper taped by their keyboard. And as the cashier scans items, the customer can bag at the same time or scan their loyalty card - overlapping these discrete tasks in a pipeline significantly improves the elapsed time.
By the numbers: payment by credit-card took around 35 seconds in all cases (cash was faster by the cashier). Scanning and bagging each item took about 6 seconds for the cashier, while it took about 23 seconds for the self-checkout customers. So there's a rule of thumb: for every three items you want to buy, the cashier will be about one minute faster than the self-checkout. If you're super-fast with the barcode scanner (I am not), you can time yourself and adjust accordingly.
Solitude
Arthur Schopenhauer once wrote, "A man can be himself only so long as he is alone... for it is only when he is alone that he is really free." And so, the self-checkout enables true freedom by avoiding any judgment about my basket of rash cream and four pounds of peanut butter cups. If being slower guarantees solitude, then maybe it's worth it.
Unfortunately, a significant proportion (3 of 11) of the observed self-checkout users hit errors like "unexpected item in bagging area", "place your item in the bagging area", and the vaguely ominous "please wait for help". This summons an employee to tell you haha, every time, right? and punch in some passcode to free you. These are generally anti-theft measures, which slightly inconvenience those dastardly criminals while majorly blowing up your plans to not speak to anyone today. [footnote 2]
8 out of 11 customers did succeed in not speaking to anyone - a 73% chance to be left alone is not awful, but it's not great either. Personally I don't actually mind saying hi and thanks to a cashier, but even if I did - I think I might prefer the certainty of a little talking instead of the anticipation of a maybe 1-in-4 chance that the machine will say, "surprise, I'm going to lock up until someone comes over to reset me and make small talk with you".
Takeaways
After I crunched the numbers, my life was never again the same. Now whenever I'm at the grocery store, I always make a direct beeline for the cashier, which saves me like, two minutes or so. At this point it's probably paid for that initial hour of soup-loitering and follow-up analysis. In a couple more years it'll also make up for me writing this blog post! Anyways, the sense of smug satisfaction I get when skipping the self-checkout is the true reward. I strongly recommend it.
And finally, a few unsolicited suggestions for any self-checkout manufacturers or supermarket owners reading this (which was the actual point of the assignment):
- Use pretty pictures to help users find the produce lookup
- Turn off those anti-theft measures on the machines, it makes the experience much worse for law-abiding customers while barely inconveniencing actual thieves
- Consider switching one-line-per-cashier to a single global queue
Thanks to my classmates Evan and Jia for being co-conspirators on this assignment.
Footnotes
[footnote 1] (back to content)
Of course, people are smart, see that one line feeds multiple machines, and will happily get into a longer line expecting it to move faster. Now we're getting into queuing theory as well as psychology, which is both interesting and too long to discuss here. For what it's worth, a good number of the supermarkets I go to in San Francisco and the surrounding area do have a single global queue for their human cashiers as well, which completely eliminates this advantage for the self-checkouts.
[footnote 2] (back to content)
The weight sensor is supposed to help prevent a thief from swapping barcode stickers from a bottle of water to an entire wheel of cheese (in order to support their pecorino addition). As The Atlantic describes, there's nothing really stopping them from ringing it up as loose bananas instead, or a case of water with similar weight, as long as they're comfortable doing it under the eye of a bored supermarket employee.
The space below is left empty so that clicking on footnotes will scroll to the correct location.