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Seems to me the big problem with any kind of retail queue is highly inconsistent service times. If you have a consistent time/ customer, it's easy to predict. A

Seems to me the big problem with any kind of retail queue is highly inconsistent service times. If you have a consistent time/ customer, it's easy to predict. As soon as you have some customers taking 20 minutes and some taking 2 minutes all the simple math goes out the window. This is why some people get so infuriated when they see the person in the front of the line break out a fist full of coupons, food stamps, or wants to pay with a check. It's also why so many businesses use a single queue with multiple tellers/ cashiers.

rahimnathwani 7y ago
"Seems to me the big problem with any kind of retail queue is highly inconsistent service times." The article mentions that as one of the two problems: "If customer arrivals were exactly evenly spaced and each took exactly 10 minutes to serve, there would be no problem." "It's also why so many businesses use a single queue with multiple tellers/ cashiers." The article implicitly assumes a single queue. But, as long as any empty queue is immediately filled by someone switching from another queue, this assumption doesn't affect the expected total # of people waiting.
SilasX 7y ago
Right, variance of wait time -- not just the mean -- is definitely a(n anti-)desideratum, for exactly the reason you gave[1]. I don't know how much emphasis academic queueing theory puts on this though. [1] To put it another way, you can assume entrants plan for the line to take less than the 95th (or whatever) percentile time; the lower you get this figure, they better they can allocate their time for other tasks.
dreamcompiler 7y ago
This happens a lot in retail, the DMV, post office, etc. The best way to model it is with a meta-process where servers randomly disappear and reappear. This also captures the infuriating phenomenon of tellers going on break or (worse) looking like they're available when they're not because they have to stop and count the till or something.

rahimnathwani 7y ago

"Seems to me the big problem with any kind of retail queue is highly inconsistent service times." The article mentions that as one of the two problems: "If customer arrivals were exactly evenly spaced and each took exactly 10 minutes to serve, there would be no problem." "It's also why so many businesses use a single queue with multiple tellers/ cashiers." The article implicitly assumes a single queue. But, as long as any empty queue is immediately filled by someone switching from another queue, this assumption doesn't affect the expected total # of people waiting.

SilasX 7y ago

Right, variance of wait time -- not just the mean -- is definitely a(n anti-)desideratum, for exactly the reason you gave[1]. I don't know how much emphasis academic queueing theory puts on this though. [1] To put it another way, you can assume entrants plan for the line to take less than the 95th (or whatever) percentile time; the lower you get this figure, they better they can allocate their time for other tasks.

dreamcompiler 7y ago

This happens a lot in retail, the DMV, post office, etc. The best way to model it is with a meta-process where servers randomly disappear and reappear. This also captures the infuriating phenomenon of tellers going on break or (worse) looking like they're available when they're not because they have to stop and count the till or something.