The point of estimates

The other day I listened to a very interesting talk by Allen Holub on the #NoEstimates movement, which I've posted about before.  It's definitely worth a look if you have some time.  Mr. Holub makes the slightly controversial claim that all estimates are evil and we should all just stop doing them immediately.  His rationale for this is essentially that estimates are made up and harmful.  And, of course, he's not wrong.

I've always been a little skeptical of the #NoEstimates movement, but the thing it clearly get right is that estimates are frequently misused and misapplied.  Just about every developer has a story about estimates being interpreted as promises, or having to work late just to "meet your sprint commitments", or skimping on quality because the sprint is about to end and you need to close out your tasks.  And we won't even get into managers who try to use estimates as a performance evaluation tool - the dysfunction of this should be obvious to anyone with any experience.

Is it the estimates?

So estimates can be used for bad things.  That's not controversial.  But that's also not a problem with estimation per se.  I guess you could think of it as the software equivalent of "guns don't kill people, people kill people."  It's not that estimates are inherently bad, it's just that they're seldom used for good.  That doesn't mean that you should abolish estimates, but it does mean that you should use them with caution.

The thing about estimates is that, while they're often just guesses, they don't have to be.  In my study of the Personal Software Process (PSP), I learned about doing estimates based on historical data.  I've even seen it work - in my last job, I reached the point where my time estimates were within about 15% of actual task completion time, which I consider to be pretty good given that the estimates were in minutes.  Granted, it doesn't always work - sometimes you have tasks that are truly unprecedented or have too many unknowns - but it can be done.

The main problem with data-based estimation is that most organizations and developers are not equipped to do it.  For one thing, it requires data, and a lot of shops don't actually collect the kind of data that would be useful.  Most developers certainly don't collect the kind of data that the PSP estimation method uses.  It also takes more time than many people seem to want to devote to estimates.  It's not that much time, but still a lot longer than saying, "well, I guess that's about eight story points".

What's the point?

The real question here is: why do you want an estimate?  What are you trying to accomplish?

When I do PSP estimates, I'm using them to gauge my performance.  I'm looking at my historical data and using that to project out time, code volume, and defect counts.  I can compare these projections to my actual results, see if my performance is consistent, and if not, analyze the reasons and look for ways to improve in the future.

Yes, these are "estimates", but not in the same sense as most teams do them.  My manager never sees these "estimates"; I make no commitments based on them; nobody depends on their being accurate; in fact, nobody but me even knows what they are.  They're a part of my task planning, so they're short-term estimates - they go out two or three weeks at most, usually more like a few days.  I start with some requirements analysis, sketch out a conceptual design, and then do the estimate based on that.  So the process of coming up with the estimate actually helps me flesh out and validate my plan, which is valuable in and of itself.

The important thing to note in the above description is that my estimates are not targets.  If I'm working on a task and it takes 500% longer than my estimate, I'm the only one who knows and I don't care.  Sure, I'll try to figure out why that task took so much longer than I thought, but the fact that "I missed my estimates" has no relevance and no consequences.

But that's usually not how it works when your boss or your project manager (or even your scrum master) asks you for an estimate.  They want you to tell them when the task will be done.  And they'll be very disappointed if it's not done when you said it would be.  And that's where the dysfunction begins....  Because even in the best of circumstances, we don't really know exactly how long s development task will take.  And we seldom work in the best of circumstances.

So...no estimates?

The interesting thing about doing PSP estimates is that, until relatively recently, I had trouble not thinking of the estimates as targets.  Process Dashboard, my PSP support tool, has a progress bar that counts down the time remaining for your estimate and then turns red when you go over the estimate.  And I would actually get upset when that bar turned red!  Why?!?  There was no reason for that - there was literally nothing at stake!  I was just psychologically stuck in the wrong mindset.  And that's the same mindset that most people get stuck in when they talk about estimates.

So I'm starting to come around to this "no estimates" thing.  I still believe that estimates can be useful and productive, but they usually aren't.  And if your company is particularly enlightened and can do estimates in a way that's productive and avoids the pathological effects associated with them, then by all means, keep doing estimates.  But most people don't work in companies like that.  And even if your company is great, you still need to be careful of the psychological pressure created by the inherent biases and preconceptions of your developers.

In other words, estimate carefully.  Consider simpler, lower precision (but not necessarily lower accuracy) methods like Mr. Holub and the other #NoEstimates advocates describe.  Don't be fooled - those are still estimates, but they at least make an effort to work around the damaging side-effects associated with traditional estimation.  After all, it doesn't matter how good the estimates are if they destroy team morale.

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