But a lot of that is nothing to do with stress created by the job role (ie the factor we're supposed to be comparing). Those other stresses - such as how good your manager is, location, the prevailing economic conditions... surely you have to discount those as not being relevant when making a strict comparison between one job role and another. Just about any job can be made stressful by introducing a terrible manager, let's put it that way. Even your dream job could be ruined if your manager is an asshat.Its heavily dependent on so many things. Store location, type of customer, what shifts you work, how well the TL/manager can run the line, PoS hardware, store size etc. etc. Heck even the economic climate can effect how stressful that job can be, working when staff are being cut and you're expected to deliver more with less resources is a pain. For example my 7-1 Saturday morning shift was nothing compared to working 5-9:30, 30mins of that evening shift pulled in more than the entire 7-1 shift.
Things that would be taken into account from your list would be shift patterns, ease of using required equipment, time pressures, etc.
I don't know how things are now, but being a till assistant was pretty darned easy for the few months I was there in school holidays. Lots of people had time and opportunity to goof around, engage in idle chatting, etc, etc.
Heck, you walk into any store today and you can find (often) store workers having a chat whilst they walk around the store, or whilst there's nobody on their checkout. There certainly are lulls, and we can all see that with our own eyes.
I find it hard to believe that checkout operators are dealing with constant emotional stresses that would need a significant increase in their pay to account for.
The physical stress of a warehouse staff is more easily measured and observed. And there is no getting around the fact that all warehouse staff will be subject to those physical demands.
Whereas it's perfectly possible for the checkout operators to enjoy their job and not find it emotionally challenging at all. Depends on their personality, and of course the factors you mentioned above which apply to all jobs and situations.
But you can't (I think) look at a checkout operator job role and say, "This job has significant emotional demands equivalent to 10 hours of heavy lifting at a brisk pace in a warehouse." None of that sentence makes any sense to me.