Fibonacci Series = Accurate Agile Estimates? + FREE Cheat Sheet

does using the Fibonacci series for

estimating improve the accuracy of those

estimates that's the question we're

going to be looking at today and stick

around to the end to get your hands on

this free agile estimating cheat sheet

my name is Gary Strom welcome to

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along with this series on agile

estimating you'll have got the message

by now that estimating is hard but some

estimates are much easier than others

we've talked previously about estimates

of absolute size versus estimates of

relative size how heavy is this is a

hard question which of these is heavier

is an easy question why is it an easy

question well it's because there's a

large difference we assume in the white

of these two when I say difference is

that the absolute difference or the

relative difference which of these two

coins is heavier which of these two

bridges is heavier I hope that answers

the question

it's not the absolute difference that's

important it's the relative difference

hold on a second one there supposed to

be an episode on the Fibonacci series I

think it's time we rolled it in actually

let's build it from scratch the first

two numbers are 0 1 1 and to get the

third we add the first two together 0

plus 1 is 1 and we carry on adding pairs

of numbers 1 plus 1 gives us 2 1 plus 2

gives us 3

two plus three gives us five and so on




34 55 89 what's interesting in this

series is the gaps between the numbers

not the absolute gaps the relative gaps

the relative gap between these two is oh

that's infinite yeah that one's a little

bit large let's move on

the relative gap between these two is

100% okay 50%

66.6 recurring percent 60%

sixty two point five percent sixty one a

bit percent almost sixty two percent

sixty one point eight sixty one point

eight after some craziness at the

beginning of the series the relative gap

between the members of the series

settles down to around 60 Warren and a

bit percent let me see if I can

demonstrate that to you a little more

visually here are the first few 0 1 1 2

3 5 ah yeah now we're at space so I'm

gonna zoom out round about sixty percent

and there's the 8 zoom out another 60


there's the 13 zoom out again 21 zoom

out once more

34 zoom out again 55 zoom out one last


89 I hope you can see that although the

bars are getting skinnier as we zoom

further and further out the relative

size between this one and this one stays

pretty well constant

the reason that the scale works so well

for estimating is that it encourages us

to stay in the realm of easy estimates

it encourages us to stay with relative

estimates to say in slightly different

terms if we are estimating two things

and their sizes their relative sizes are

not sufficiently different then we

consider that they both have the same

size which brings us right back to the

question that we started with today does

the Fibonacci series lead to more

accurate estimates I think the answer

has to be no if anything what it does is

protect us from attempting to make

accurate estimates it keeps us in the

realm of making rough or broad estimates

so I'm curious do you use the Fibonacci

series for your estimate I'd love to

know let me know in the comments below

and finally today there's the small

matter of the cheat sheet that I

mentioned at the beginning the agile

estimating cheat sheet you'll find a

link in the comments below click the

link follow the instructions and it's

all yours thank you very much for

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