Grocery store checkouts
For the past year or so, I’ve been timing how long it takes for me to go through the checkouts at our grocery store to see which is faster.
The methodology is quite simple. Once I’ve got all my groceries, I go to the same spot near the checkouts. To avoid biasing myself, I check my cell phone to determine whether to go through the self checkouts or the normal checkouts. Because my cell phone lacks a random number generator, I check the last digit of the time: an even digit means I go through the normal checkout and an odd digit means I go through self checkout. I then start the stopwatch and time how long it takes for me to go through the checkout and leave the store.
I’ve got 31 data points and have finally decided that if one type of checkout is faster than the other, the difference is small enough to not really matter. Here’s the scatterplot:
A sample size of 31 is unimpressive, to be sure, but it’s large enough that I can finally rest easy knowing it would be a waste of time to collect more data. Trying to get out of the grocery store in the fastest way possible seems to have more important factors, such as the number of jerks ahead of you in line.
As a side note on how that scatterplot is presented, it probably would have made a lot more sense to measure the time taken as a function of how many items I bought, rather than the cash value of the items I bought. I’m far too lazy to count things, though.
So, from now on I’ll be deciding on self checkout versus normal checkout based on how social I’m feeling. I suspect that means I’ll be using the self checkout a lot.
In my experience, the people in front of you and the competency of the checkout clerk are the biggest factors.
That said, I may gather some data for myself, just to see how it turns out.
Don’t forget the bag clerk factor. Having that extra clerk packing groceries at least gives the illusion of speeding things up.
Check this out. Someone managed to get some real data from a store manager.
From his observations every person in line adds 48 seconds to the total amount of wait time, whereas item the person is purchasing adds 2.8 seconds, so even if a line has one fewer person but <17 extra items on the conveyor you’re better off in the line with one person less.
Although it feels counter-intuitive, I now use this approach all the time, and I frequently end up not choosing the express lanes. Sometimes I mark my position against another lane or two (especially if I queue up simultaneously with another person), and almost without fail I end up making it through the checkout faster by utilizing the data above.
Our grocery store doesn’t have self-checkout lanes yet, but I suspect similar principles apply.
My vision of the ultimate grocery store experience: click on items online, robot optimally packs my items into a cube, I either pick them up or have them delivered. Why oh why do we still have to walk around a store and stand in line. Ridiculous.
I’ve noticed the express-lane is pretty stupid. A break-even point of 17 doesn’t make it always useless, I guess. Every now and then there’s someone buying like $200 worth of groceries, but that doesn’t come up much.