Given a set of high level epics what's the best 'guestimate' we can come up with to scope the software system appropriately given a time-to-market window? What are some good/best practices for this high level estimation (I know it'll be way off, but atleast be better than "I don't know"). So we don't yet know who (i.e. which teams) would be developing this system, so we can't just drill down all stories and play planning poker with them. I'm looking for an initial and a somewhat SWAG at this level of granularity.
Here are some of the techniques and their criticisms (IMO):
- Play a high level planning poker along with tech leads in the company - have scores of 40, 80, 120 etc., Issue: No one knows what the heck they are talking about IMHO - it's easy to state whether a story is 1,2,3,5, 8 etc. but not many seem to understand the difference between an 80 or a 120 - folks would rather just go with higher estimates to be conservative (better to just guess a random number)
- Use parametric modeling tools like COCOMO or SLIM and the like. Issue - input is either SLOCs (which are just pure guesses and even more difficult with disparate technologies) or Function Points (FPs - not quite easy to do either). Although they may give good estimates as outputs, they are only as good as their inputs
- Work/Epic Breakdown Structure - I feel this is the best 'right' balance between the above two extremes i.e. breakdown epics, top-down into features to get an idea of scope. (one can also quickly come up with high-level one line stories for each feature (or if feature = story, in your case, then high-level features). Since stories usually range from 1 - 13 in the fibonacci scale (i.e., quite common IMHO to see stories in this range), just give every story/feature a score of 5 and aggregate them to get the score of the epic for a rough initial estimate (since there will be quite a few less than 5 as there will be more than 5, I feel 5 is a good mid-point/average to go by).
The last bullet method is what I'm leaning towards but am more than welcome for suggestions/inputs on what have you practiced and been sufficiently happy with and avoiding estimation paralysis - yes the estimates will be refined later on, but we still need a very high level view to balance expectations and plan accordingly :)