Earned value: what's wrong with MS Project

[Jan M.]

Hi,

I made a very simple project in order to understand how MS Project is
calculating earned value:

1 task
Work: 8h
Duration: 1 day
Resource: 1 person at 100%
STD rate: 1$ per h

I applied the task usage view and entered 4 hours of real work on the first
day. Then I modified the remaining work a couple of times to see the effect
on BCWP. What I found out was quite surprising:

BCWP of the assignment was different than BCWP of the task! I didn't
expected this since there is only one resource assigned to the task.
Shouldn't the assignment and the task show the same BCWP in this situation?

Can anybody explain?

Thanks

Jan M.

 

[JulieS]

Hi Jan,

I believe the difference you are seeing between Task BCWP and Assignment
BCWP in the Task Usage View is the difference between how each value is
calculated.
When looking at Task BCWP, the calculation is based upon the % complete
which as based upon a task's *duration*. When you entered 4 hours of actual
work, Project added 1/2 day of remaining duration to what was originally a 1
day duration task. The % complete (% of duration) for the task is 67% and
the BCWP for the task is $5.33

When looking at assignment BCWP it is calculated on % work complete. The
assignment is only 50% complete and the BCWP is $4.00.

Hope this helps. Let us know how you get along.

Julie

 

[Jan M.]

Thanks Julie.

I think you are right. MS Project seems to be using % complete at the task
level but % work complete at the assignment level. I still can't think of one
good reason to be inconsistent in the calculation method. Can you?

Personally, I do prefer % work complete because value is earned as work is
accomplished, not as time passes by. Recently, I had a case where the
distribution of work was skewed to the right. Since we managed to put in much
work than planned in the early phases of the project, earned value based on
duration was not representative of the reality.

I've been looking for a way to use % work complete in earned value
calculation. I have tried exporting to Excel, but unfortunately, neither %
work complete nor remaining work is available as a "timescaled" field.

If you were to use % work complete instead of % complete to calculate earned
value, what would you do?

What do you think about Microsoft calculation based on % complete(duration)?
Does it make any sense to you?

Regards

Jan M.

 

[JulieS]

Hi Jan,

The only reason I can come up with the inconsistency in the calculation is
because assignments don't have durations. If you add the % Complete field to
the Task Usage view, you'll see there are no entries for the assignments -
only the tasks. (Only a wild guess on my part.)

As far as using % Work Complete for Earned Value calculations, there is a
work-around. In Project 2002 & 2003 you can use Physical % complete as the
basis for earned value. (Tools>Options>Calculation tab, click the Earned
Value button.) The Physical % complete field is not calculated - in other
words, you need to enter the data yourself. But you could copy the % Work
complete data into the Physical % Complete field. Also add the [Earned Value
Method] field to the view and make sure the EV Method is set to Physical %
Complete for the tasks. (I'd use the fill handle to copy.)

Hope this helps. Let us know how you get along.

Julie

 

[Jan M.]

Hi Julie
I have already tried copying % work complete in physical % complete. But the
problem I encountered was that there was a discrepency between BCWP in earned
value table and BCWP in the timescale. I think your "wild guess" just gave me
the explanation:

In the earned value table, BCWP task is the same as BCWP assignment. In the
timescale, BWCP task is always calculated with % complete even if the BCWP
assignment is calculated with physical % complete:which means both values
could can be different. The difference between BCWP task and BCWP assignment
in the timescale is the reason of the difference between BCWP task in the
earned value table and BCWP task in the timescale. The use of % complete as a
method of calculation for earned value prevents this discrepency because BCWP
is calculated the same way everywhere.

If I am to use physical % complete and want to export to Excel to graph CPI
and SPI, I will get different values than those shown in MS Project. I think
it is a major issue that limits the use of physical % complete in MS Project.

Regards

Jan

Hi Jan,

The only reason I can come up with the inconsistency in the calculation is
because assignments don't have durations. If you add the % Complete field to
the Task Usage view, you'll see there are no entries for the assignments -
only the tasks. (Only a wild guess on my part.)

As far as using % Work Complete for Earned Value calculations, there is a
work-around. In Project 2002 & 2003 you can use Physical % complete as the
basis for earned value. (Tools>Options>Calculation tab, click the Earned
Value button.) The Physical % complete field is not calculated - in other
words, you need to enter the data yourself. But you could copy the % Work
complete data into the Physical % Complete field. Also add the [Earned Value
Method] field to the view and make sure the EV Method is set to Physical %
Complete for the tasks. (I'd use the fill handle to copy.)

Hope this helps. Let us know how you get along.

Julie

Thanks Julie.

I think you are right. MS Project seems to be using % complete at the task
level but % work complete at the assignment level. I still can't think of one
good reason to be inconsistent in the calculation method. Can you?

Personally, I do prefer % work complete because value is earned as work is
accomplished, not as time passes by. Recently, I had a case where the
distribution of work was skewed to the right. Since we managed to put in much
work than planned in the early phases of the project, earned value based on
duration was not representative of the reality.

I've been looking for a way to use % work complete in earned value
calculation. I have tried exporting to Excel, but unfortunately, neither %
work complete nor remaining work is available as a "timescaled" field.

If you were to use % work complete instead of % complete to calculate earned
value, what would you do?

What do you think about Microsoft calculation based on % complete(duration)?
Does it make any sense to you?

Regards

Jan M.

 

[JulieS]

Hi Jan,
Your reply started me "playing" with EV based upon % complete & Physical %
complete and I found an interesting "feature." On tasks that were 100%
complete (both Work %, and Physical % complete) I found that I could make the
BCWP values disappear completely, both in the EV table and the timescaled
view.

I added the EV Method field to the EV table applied to the Task Usage view.
When I changed the EV Method back and forth for individual tasks and forced a
recalculation (F9), the BCWP values would disappear if the EV method was set
to Physical % complete and then re-appear if I set the EV method back to %
Complete and forced a recalculation.
This does make me wonder (like you) how valid the data is.
Hmm.... I think this one is going to keep me awake for a few nights......

If anyone has some thoughts, I'd be interested in hearing them.

Julie

 

[Jim Walker]

I use MS/Project 2000 and have seen similar problems. I am sorry to hear
that problems persist in Project 2003.

I produce a number of Earned Value reports by exporting Project data to
Excel. I am always careful when using an advanced feature of Project for the
first time so I performed my own Earned Value calculations using macros as a
cross-check for Project's calculations. I found the same problems that Jan
describes but found that, with care, I could make the task-level results
perform correctly. Assignment-level numbers remain problematic though many
of the problems look like rounding issues.

I plan large I.T. projects (50-80 people, 12-24 months duration). Here are a
few things I do to get reliable EV information:

- Avoid assigning multiple resources to a single task because Project
provides more robust and reliable analysis of task data than assignment
data. For instance, exporting task data to Excel using maps is very easy. It
is more difficult to export assignment data.

- If each assignment is set up as a task then Earned value calculations can
be used at the task level. If you create a task for every assignment, your
plan may look longer but it will be much easier to analyse.

- Earned Value fields are severely impacted if you change resources on a
task by any method other than the "Assign/Reassign Resources" dialog. For
example, if you change the resource using the drop down list in the resource
names column then baseline data will look okay but BCWS and BCWP will be
completely destroyed.