We have been thinking about comparing product size/effort at least roughly and this is what some suggested:
- There are multiple products, each with one scrum team
- All the scrum teams estimate their stories relative to a common reference story. Therefore, e.g. in Project A, they look at their story and estimate it as requiring twice as much effort than the reference story.
- In the end, all the projects are estimated with relation to this reference story and are somehow comparable in terms of expected effort - if one project has 200 SP and the other 400 SP, it could be expected that it is roughly twice as much WORK.
- Individual teams have their own velocities, nobody compares that because productivity is of course different.
An analogy: when digging a hole, I can say that a hole 10 meters deep will be 10x more work than a reference hole (which is 1 meter deep). One team will use an excavator and dig their 10 meters deep hole in 30 minutes. The other team will use a spade and spend 2 hours digging their 1 meter deep hole. But the amount of work done is still the same and can be compared (1 vs 10), regardless of productivity. Sure, SW is far from that simple to estimate but it should not be completely off.
Is there a problem with that? To me it seems fine as the teams only need to compare their work with a common reference story and assign points relative to it (as they would do when estimating using with their own reference story). It is completely fine if team A takes a day to finish a story point while team B takes two days, what matter is that the estimation is consistent.