Monday, 27 September 2010

Checkout queues - not quite what you thought...

Queuing is important. I know you all hate it but it really is important. I’ve blogged before about this matter – in a little moan about the value and importance of differential pricing. So now we’re going to consider the checkout.

Now one of the things about queues (other than the fact that the other queue always moves faster) is that we make an assumption that the shorter queue will take less time. Now this is – on the basis of the information available to us and our common sense – a rational decision. However, it could also be wrong.

Here’s a mathematician studying the issue:

There are easily a dozen variables affecting the line speed that have nothing to do with the number of customers in each line or the number of items in their baskets.

And the other variables tell us that:

Cheque is slower than credit which is slower than cash – not really a surprise and perhaps explains (the rapidly vanishing) cash-only lines

The y-intercept is non-zero – in other words:

It should take you zero seconds to purchase zero items but you can't ignore the fixed time cost of the pleasantries ("Hi. How are you doing? Do you need any help out?") and the transaction itself.

The express lane isn't faster.

You attract more people holding fewer total items…when you add one person to the line, you're adding 48 extra seconds to the line length … without even considering the items in her cart.

So this answers the question about “express” queues – they are not a strange privilege for people who aren’t buying very much but a means by which these people are removed from the main queues – thereby speeding up your passage through with a trolley while making no difference to the customer with but a few items. In truth the rational decision is to separate different queues (i.e. different customer behaviours) in the knowledge that the asymmetry of understanding will improve the rate of throughput. Not only does this make your customers happy but it also reduces the supermarket’s costs (which – in a benign cycle of benefit – further increases the customers’ happiness by helping reduce prices).

Today, there is a further complication with the introduction of self-service checkouts. Again these will remove some customers from the checkout queues (and leave them standing frustrated while the machinery doesn’t work). And the jury is out on this wondrous technology:

It’s easy to see why retailers are turning to more and more self-service kiosks. They put the customer in control, they can reduce operational costs and they save on staff costs. When they are designed well they can improve customer experience because customers grab their goods and leave the store with minimal fuss. When they are designed poorly, they can be time consuming and frustrating having a negative impact on customer experience.

And they might not have cut queues either (although this might not have been the point):

Figures compiled by The Grocer magazine show that average queuing times for staffed tills at Tesco and Sainsbury's, the retailers with the most self-service checkouts, have increased over the past two years. At Tesco, which has 6,000 self-service checkouts in its 1,200 stores, the average wait for a staffed till lengthened from 5min 15sec in 2008 to 5min 42sec this year. Sainsbury’s saw a smaller rise, from 5min 30sec to 5min 35sec.

Although the supermarkets say these figures are nonsense (and they do seem to originate in some way from USDAW, the shopworkers’ union who aren’t going to be in favour of automation). My guess is that there's a befefit to be gained but both the technology and also the customer's familiarity have yet to reach the point at which that benefit is realised.


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