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## Re: [XP] Units of time for estimates

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• ... I m wondering where he got the idea that they were better. Where did he find that? ... Ah, sounds like a local preference. Makes sense, but read on ... ...
Message 1 of 41 , Jun 29, 2001
Responding to Torben Wölm (01:36 PM 6/29/2001 +0200):
>I got a hard question from my manager the other day:
>
>"Why are 'points' a better measure than 'hours'?"

I'm wondering where he got the idea that they were better. Where did he
find that?

>The only thing I could come up with as an answer was, that I felt easier
>giving a story 1, 2 or 3 points instead of 30, 60 or 90 hours.

Ah, sounds like a local preference. Makes sense, but read on ...

>Do you have better answers?

I prefer time (actually days, because hours are too small and suggest a
level of precision that is not there. Half or quarter days is plenty accurate.)

The "points" or "gummi bears" idea was invented by Joseph Pelrine, who was
at the time working with a team who feared to mention ideal time, fearing
that it would be held against them when it took an average of 2.5 days to
do work estimated at half a day. So they called them gummi bears and
measured that it took them 2.5 days, on the average, to do one gummi bear
of work. This is clearly sufficient to do all the planning stuff, being
just a constant of proportionality between gummi bears and ideal time.

Both work equally well in the long term. Teams even somehow converge to
give things the same number of points, without ever formally defining them.
But to me it's easier to get in touch with time estimates "We could do that
in a half a day if the bastards would leave the two of us alone", and then
to use velocity to figure out how many "days" work the team can do in an
iteration.

>Background info:
>
>This is a returning issue with my manager, at every iteration planning
>meeting. The team uses points for estimates, and I must then convert our
>points to hours so our manager gets it.
>
>The problem is that we discuss everything (in the team) using points. We
>measure hour velocity in points. But every 2 weeks I have to do this
>calculation and remember the factors and arguments.
>
>The problem comes from our "IT Masterplan" were everything is calculated in
>hours. All estimates are in hours and all resources are registered for
>available hours. (And I know this makes no sense -- My estimates will not
>hold for a resource in a totally different part of the organisation, but
>apparently this is how management wants it. To them every resource is
>interchangeable and estimates are absolute).

It's wonderful to have a Masterplan. If management is trying to use 30
hours to mean 30 elapsed hours, then they're missing an opportunity to have
better estimates.

The time it takes to do something is a function of (at least) two variables:

1 difficulty: how hard the thing is in some absolute sense: (two-column
reports are x% harder than one-column reports)
2. velocity: how fast the existing team (or individual) is at doing those
things.

So we might all agree that this feature is twice as hard as that one. But
you might do it in one elapsed day and I might do it in two. This might be
because you are better than I am at programming, or it might be because I
have two other jobs to do in the company, or it might be because we have
more meetings in my department than you do in yours.

Now all those reasons are interesting and worth looking into, to make
better hiring decisions, and to improve the process.

BUT ... for management's purpose of knowing when things will be done,
breaking out the two dimensions of difficulty and velocity gives better
predictions, better insight to when things are slowing down, and a better
focus for process improvement.

So ... it might be worth it to see if you can get your manager to look at
difficulty and velocity separately, because it will help the manager manage.

If he can't get on board with it, then you need to track velocity (which
you should anyway) and use it to convert the numbers. Whether your team
estimates in points and converts, or whether you do it on the fly, you're
going to have to give the management what they want.

Or so it seems to me ... does that help at all?

Ronald E Jeffries
http://www.XProgramming.com
http://www.objectmentor.com
• bill..just wanted to thank you...i was able to take a look at their website..looks very interesting..i ll have to drop them a line to find out when they will
Message 41 of 41 , Jul 23, 2001
bill..just wanted to thank you...i was able to take a
look at their website..looks very interesting..i'll
have to drop them a line to find out when they will be
meeting..thanks once again..nicky

--- wecaputo@... wrote:
>
> check out these resources for CHAD (the Chicago
> Agile Developers):
> http://groups.yahoo.com/group/chicago-agile-dev
> http://brain.cs.uiuc.edu/CHAD
> http://www.objectmentor.com/chad.htm
>
> Best,
> Bill
>
>
>
>
>
> Nicky Petrila
>
>
> <pirates95@ya To:
> extremeprogramming@yahoogroups.com
>
> hoo.com> cc:
>
>
> Subject:
> [XP] Are there any XP meetings in Chicago area?
>
> 07/19/2001
>
>
> 01:53 PM
>
>
> Please
>
>
> respond to
>
>
> extremeprogra
>
>
> mming
>
>
>
>
>
>
>
>
>
>
>
>
> hi out there..i was wondering if there are any
> meetings in the chicagoland area in regards to
> XP...pls let me know..nicky
>
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