I recently did some statistics on the estimates of our two scrum teams.
These graphs plot "original estimate" against "actual time spent" (note that logging time spent is much less objectionable, in a scrum sense, than using actual-time units for planning).
Estimation history (logarithmic scale)
Estimation history (linear scale)
It seems to me that the resulting effort has very little correlation to the original estimates. I had of course expected overlaps, and maybe overlaps between only adjacent estimates, but I certainly don't feel that it makes sense to have 1-2-3 all touching the very low end and the high end.
5│ ══════════════ 3│ ═════════ 2│ ══════ 1│════ └─────────────────────────── My expectation: Partially overlapping estimates
Of course, estimates are crude, and occasionally things blow up, but to me this data screams "we suck at estimating" which to some reasonable extent is okay but I feel that the data displayed here is far beyond reason. I want to make an "estimation workshop" with the teams in order to come up with a better culture for estimates, but I want to make sure I have a reasonable frame of reference for it. So...
How consistent can estimates be expected to be? Is my "expected" graph way unrealistic? What, then, should I expect?
Edit: Yes, we have acceptance criteria and a "Definition of Done" (including tests, reviews, etc), but they may be insufficiently policed. Our planning poker usually shows cards of adjacent size (no huge gaps), but even so the gap is between the agreed-upon outcome and the actual size.