I think teams can estimate successfully with either set of values as each exhibits attributes of Weber’s Law. These days I remain fairly impartial between the two sets of values. Their discussions were not always “Is this one 60% more effort?” Those seemed like healthier discussions, even though I had no way of measuring that. That concerned me slightly because I didn’t see it with teams using the modified Fibonacci sequence. came from being in a lot of meetings with the latter sequence in which discussions were always “Is this product backlog item double the size of the other one?”Īll discussions were about whether something was double, quadruple, etc. My slight preference for 1, 2, 3, 5, 8, 13. Once that sequence began to appear on thousands of decks a year, the sequence gained popularity at the expense of simply doubling the values. At the time, I just slightly favored the modified Fibonacci sequence. To keep printing costs down, I had to choose between these two sequences. Most teams had a strong preference for one or the other, but I could find no clear evidence that either sequence was better than the other.īut in 2007, we began printing Planning Poker Cards, which we sold at cost, distributed at various agile events, and that I use in some in-person courses. Up until 2007, teams I worked with experimented with both the modified Fibonacci sequence and a simple doubling of numbers-1, 2, 4, 8, 16, 32.Įach worked equally well. Experimenting with Planning Poker Sequences Estimates such as 40 and 100 could, perhaps, be thought of as extreme values. This wasn’t a violation of Weber’s Law because Weber’s Law has been shown not to hold at extreme values. This was much larger than the 62% of the Fibonacci sequence. Those worked well because they represented 100% and 150% increases over the preceding numbers. That led to experimentation in which we introduced 40 and 100.
THEBRAIN 9 TRACKING TIME ESTIMATES FREE
Once we’d deviated from the Fibonacci sequence once, we felt free to do so further. This led us to start using 20 rather than 21. Stakeholders would look at the 21 and be impressed that we called it 21 rather than rounding it to 20 or even 25. Ultimately, though, we learned that an estimate of 21 implied a precision we couldn’t support. Modifying the Fibonacci SequenceĮarly agile teams I worked with made use of this and estimated with the real Fibonacci sequence. So, the Fibonacci values work well because they increase by about the same proportion each time.
After the two (which is 100% bigger than one), each number is about 60% larger than the preceding value.Īccording to Weber’s Law, if we can distinguish a 60% difference in effort between two estimates, we can distinguish that same percentage difference between other estimates. The values in the Fibonacci sequence work well because they roughly correspond to Weber’s Law. (I know I can’t.) And if you could, it would mean you should be able to distinguish between a 1.00 kg weight and a 1.05 kg weight, as that would also be 5%. The difference between 20 and 21kg, however, is only 5%. You can probably distinguish the weight of items that differ by 100%. The difference from one to two kilograms is 100%.
Weber’s Law states that the difference we can identify between objects is given by a percentage. But you would have a much harder time identifying the heavier of the two weights. They are the same one kg difference as the one and two kg weights. Imagine instead being handed a 20kg weight and a 21kg weight. The two kg weight will feel noticeably heavier. With one in each hand but not able to see which is which, you can probably distinguish them. Imagine being handed two weights-one is one kilogram (2.2 pounds) and the other is two kilograms (4.4 pounds). It’s because numbers that are too close to one another are impossible to distinguish as estimates. Years ago I began having teams estimate with a modified Fibonacci sequence of 1, 2, 3, 5, 8, 13, 20, 40 and 100. The traditional Fibonacci sequence is 1, 2, 3, 5, 8, 13, 21 and so on, with each number the sum of the preceding numbers. If you’ve estimated with Planning Poker, you may very well have used cards with either the Fibonacci sequence, or a modified Fibonacci sequence.
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