How does relative estimation work?
Can Harry Potter teach us how to use
relative estimation for forecasting the
size of product backlog items in a
Microsoft Business Application backlog?
That's a great question. I'm glad you
asked. Hi, my name is
Neil Benson from the Customery Academy.
My son, Jensen, recently completed his
first Harry Potter book, and it
reminded me of a useful metaphor about
relative estimation using Harry Potter
books. This is J.K.
Rowling's Harry Potter Complete
Collection box set, published by
Bloomsbury in English in October 2014.
There are seven books in the box set.
Imagine this was the product backlog for
your Power Apps or Dynamics 365
application, and these seven books were
un-estimated user stories, you can look
at the spine of each of the books and
you can see that they're different
sizes. Book one, The Philosopher's
Stone, and book two, The Chamber of
Secrets, are the same size.
Book three, The Prisoner of Azkaban, is
about 50 per cent bigger than book one
or two.
Book four, The Goblet of Fire, is nearly
twice as big as book one.
Book five, The Order of the Phoenix,
looks like it's the biggest in the
series, twice the size of book one.
Book six, The Half-Blood Prince, is
about the same size as book four, and
so is book seven, The Deathly Hallows.
There that's a relative estimation
using the Harry Potter series.
How easy was that?
A kid could do it...
All right, Jensen, tell me about the
book you've just read.
I've just read, Harry Potter and The
Philosopher's Stone.
That was book number one.
It's book number one, and this is what
it looks like on the front cover.
How big is that compared to book two?
It's about the same size.
So, compare those two.
Do you reckon it's about the same? Yeah,
cool. What size is book three?
Book three is about one and a half times
the as thick as book one, and this is
the front cover for book one, I mean,
book three.
OK, then what's next book four?
How big is book four compared to book
one?
It's about twice the size.
All right.
Well, nearly twice the size.
Not exactly twice the size.
That's alright. And then what's the
next one? Book number five.
Book five is twice the size of the first
book.
Is it more than twice the size?
Probably not.
Probably not, but it's about twice the
size. It's called The Order of the
Phoenix? All right.
What's next?
Book six.
Book six. How big is that compared to
book one?
It's about the same size as book four.
OK, and then book number seven?
Book seven is the same size as book four
and six.
OK.
Once we've estimated the size, we can
derive the duration.
To derive the duration, we multiply the
size by our velocity.
Just like in your physics class: d
divided by v equals t.
In Harry Potter terms, to figure out
how long it will take to read the book,
we divide the size of the book by our
reading speed. Let's see what Jensen
has to say about how long it'll take to
read.
And tell me how long did it take you to
read book number one?
About a month.
About a month. About four weeks.
Yeah.
And how often were you reading?
About an hour a day if you combine all
my reading. If you combine all my
reading.
Yeah. So if you put all your time
together during the day, a few minutes
here and there would add up to about an
hour.
Yeah.
And so how long do you think it's going
to take you to read book two.
About the same amount of time.
And then by the time you get to book
seven, do you think you'll be reading
the same speed?
Probably a bit faster.
A bit faster, so you'll be even quicker
when it comes to reading books seven?
Yeah, I might take a month and a half
instead of just two months.
Because it's twice the size but you
might be in a month and a half.
That's amazing, Jensen. And I really
appreciate you telling us about your
reading. If Jensen used book points to
represent the size of the books and
four was his baseline number of book
points for the size of book one, The
Philosopher's Stone, here are his
estimates for the size of the other
books: Chamber of Secrets, four.
Prisoner of Azkaban, six.
Goblet of Fire, seven.
Order of the Phoenix is an eight.
Half-Blood Prince, seven.
Deathly Hallows is also a seven.
Jensen said it took him a month to read
The Philosopher's Stone, so let's say
his velocity is four book points per
month. Remember, the divided d by v
equals t.
Or, four book points divided by four
points per month is one month.
We can now calculate how long it will
take him to read each book.
Chamber of Secrets, one month.
Prisoner of Azkaban, one and a half
months. Goblet of Fire, about a month
and three weeks. Order of the Phoenix,
two months. Half-Blood Prince and
Deathly Hallows also about one month
and three weeks each.
The total is 10.8 Months.
But Jensen also said that he thinks his
reading speed will increase as he
spends more time reading and his skill
improves. So if his reading speed
increases to four and a half points per
month for books four, five and six, and
five book points per month for book
seven, then it'll take him 9.8 months
to read the entire series.
Just like Jensen did, I'd always
recommend using a high velocity and a
low velocity to give your grown ups a
range when they ask you 'Hhow long
will it take to get done?'.
So there you have it.
If Jensen can use relative estimation to
forecast how long it will take to read
the complete Harry Potter collection,
I'm sure you can use it to estimate the
size of your Microsoft business
application backlog. If you found this
video helpful, I'd love it if you
subscribe to my YouTube channel down
below. In the meantime, keep
sprinting. Bye for now.
Hey, by the way, what age are you?
Seven, but I'm turning eight in five
days.
Oh, happy birthday, Jensen!
Thanks.
