Resource Assignments

[Bill]

I have created a project schedule by first listing all
the tasks then inserting the durations for each task.
The task type is Fixed Units for the entire schedule.

One of my tasks has a duration of 8 hours. While I
expected the resource to work on the task would have a
100% units, the best person available to do the task has
50% units availability. When I assigned this person with
50% units to the 8 hr task, I expected the duration to
change from 8 hours to 16 hours since the assigned
resource can only spend 50% of their time on the task.
However, the schedule still shows 8 hours duration even
though the assigned resource at 50% can only work four
hours on the task each day.

Why doesn't duration change on tasks when the assigned
resources have less than 100% units? Any advice will be
appreciated.

 

[JulieD]

Hi Bill

because that's the way Project works

there are three factors at play when dealing with resource assignment ...
and these are combined in the following formula
work = duration x units
(this can be expressed colloquially as man hours = duration x number
resources)

now when you created your tasks you assigned a duration, then you assigned a
resource and project did its bit by calculating work ...
work = duration x units
work = 8hrs x 50%
4hrs = 8 hrs x 50%

the "problem" lays in the definition/usage of max units ... if you say a
resource can only work at a max units of 50% then when you assign them to a
task project will only assign them at a maximum of 50% ... which means that
you're giving them an 8hr period to do 4hrs of work.

If however, you want them to do 8hrs of work but only to work part-time on
the project the best approach is to edit their calendar to only work 50% of
the time and then put in a max units of 100% when you assign them to a task
you'll end up with the following
work = duration x units
work = 8hrs x 100%
8hrs = 8hrs x 100%
and the Gantt Chart will show a longer period on it to cater for the fact
that they are available only half a day - you will also see this in the
resource usage view.

hope this makes some sense

Regards
JulieD

 

[Steve House]

In a nutshell, this behavior is a consequence of the fact that Duration
hours and Work hours are each measures of two entirely separate concepts and
are not interchangeable. Duration doesn't in itself convey any information
about the amount of work a task requires and so Project doesn't assume
anything about the amount of work for a task until *after* you have made the
resource assignments. When you assign someone, no matter what effort
percentage you assign, Project assumes that percentage is what you knew you
were going to assign when you came up with the original duration estimate
and so it calculates the work accordingly. So in your case, you estimated
the duration at 8 hours. If you assigned someone 100%, Project says "8
hours at 100% means the task will require 8 man-hours." But if you assign
someone at 50%, Project says to itself "hmmm - 8 hours at 50% means it's
only a 4 man-hour task." In either case, as you observed, the duration
stays at 8 hours. Now if you *edit* the resource assignments after the
initial one, changing the 100% to 50% for example, Project will adjust the
duration. But it never does it when you put the first resource(s) on. The
best approach is to think ahead to the resource assignments you're likely to
make when you're building the WBS and set the duration estimates
accordingly. But that might not always be possible and if you're using the
notion of One Full Time Equivalent to estimate the durations, assign your
resources at 100% and then *edit* the assignment level to reduce it to the
available 50% and Project will adjust the duration for you.

 

[JulieS]

Hi Bill,

In addition to the great information provided by JulieD
and Steve, I suggest you work with the task form visible
at the bottom of the Gantt chart. Go to Window --> Split
and this will place the task form at the bottom of the
Gantt chart. If necessary, format the task form to show
resources and precessors. (Right click in the form and
select the format from the shortcut menu.) You may then
edit work, duration, or units and quickly see the effect
of the edit.

Hope this helps,
Julie

 

[Bill]

Thank you Julie, Steve, and Julie for the information, it
really helped.

 

[JulieS]

Hi Bill,

Glad to know, and thanks for the follow-up
Julie