The Easy Way to Estimate Quickly and Accurately
Transcript
What should you do when the estimate you want to assign is between the values your team has agreed to estimate with?
When estimating with story points, most teams use a predefined set of values that does not include every possible number.
For example, teams commonly use powers of 2, 1, 2 4, 8, and 16, or a Fibonacci sequence, one, two, three, five, eight, 13. By intentionally leaving some
numbers out of the set of acceptable estimates, team avoid bogging down in discussions of, for example 15 versus 16. Estimating to that level of precision
would be extremely difficult and time consuming, most likely not even possible.
But what should you do when you think the right estimate is not one of the teams agreed upon values?
The answer comes from thinking about water buckets.
Suppose you have 10 liters of water you need to store.
You also have an 8-liter bucket and a 13- liter bucket.
Which bucket would you store 10-liters of Water in?
the 13 liter, right?
Ten liters does not fit in an eight liter.
The water would overflow and spill out.
Extrapolating further, you'd use the 13-liter bucket for all amounts of water from 9 liters through 13 liters.
Once you hit 14 liters, though, You'd again move to a bigger bucket.
It's the same with the values you use when estimating stories.
Think of each value as a bucket, a value bucket is used for ALL stories between that value and the next lower value.
For example, suppose you're estimating with a sequence that includes 8 and 13. Anything larger than 8, and up to 13, should be called 13 story points.
That is, each story point value is implicitly arranged, just like a bucket can hold a range of amounts of water.
The trick is to choose the right bucket.
For accurate estimating and planning, teams need to understand that their job is not to put an estimate on a product backlog item.
Their job to is put the story in the correct bucket, Yeah, I know that in both cases, someone grabs a pen and writes a number on a story card.
But the goal is to find a bucket just large enough to hold the whole story.
When estimating, ask the team to picture a set of buckets in front of them, labeled 1, 2, 3, 5, 8, and 13, or whatever sequence the teams uses.
And then ask team members to pictures themselves throwing cards into the buckets.
This helps team members move away from the feeling that estimates need to be perfect and precise.
They don't.
Product backlog items merely need be thrown into the right bucket.
You might be concerned that this rounding up of estimates could lead to inflated or padded schedules.
Let me explain why that usually won't happen.
Consider a product backlog item that you believe should be 10 points, but you're using the modified Fibonacci sequence and are following this rounding
up strategy I recommend.
And so the bucket you throw the product back log item into will be 13. Next, let's assume that at 13 points the item is too big to bring into a sprint.
And so the team splits it into smaller stories.
Perhaps they split it in to three smaller stores, which they estimate as 5, 5 and 2 points.
Notice what happened there with the numbers?
The three small stories add up to 12 points, that's one less than the 13 point estimate you actually put on the larger story.
But it's two more than the 10 you really thought was the right estimate for the initial large story.
By forcing the estimate into the next larger bucket, you've improved the likelihood of accurately predicting the delivery date of this project.
If you had rounded down to the lower estimate, eight, the project would be four points late.
the project would be two points late.
Instead, by using the estimate values as buckets and rounding up, you've made it more likely you'll deliver this project on time.
But couldn't the 10-point story have turned out to really be eight points?
Sure, but it could also have turn into 14, 15, or any other number of points.
If you're interested in really gooding good at estimating, check out my video course, Estimating with Story Points.
I've linked to it in the description.