Q:

How to indicate reliability when reporting availability of competencies

We have employees with competencies:
Pete      Welder
          Carpenter
Melissa   Carpenter      

Assume they both work 40 hours/week, and have not yet been assigned work.
We need to report the availability of these competencies, expressed in hours.
As far as I can see now, we can report this in two ways:
Method A. When someone has multiple competencies, count them both.
Welder    40 hours
Carpenter 80 hours

Method B. When someone has multiple competencies, count an equal division of hours for each
Welder    20 hours
Carpenter 60 hours

Method A has our preference:
- A good planner will know to plan the least available competency first. If 30 hours of welding is planned, we will be left with 10 welder, 50 carpenter.
- Method B has the disadvantage that the planner thinks he cannot plan the job when 30 hours of welding is required.
However, if we report this we would like to give an estimate of the reliability of the numbers for each competency, i.e. how much are these over-reported?
In my example A, would I say that carpenter is 100% over-reported, or 50%, or maybe another number?
How would I calculate this for large numbers of competencies?
I'm sure we are not the first ones dealing with this, is there a 'usual' way of doing this in planning?
Additionally:
- Would there be an even better method than A or B?
- Optionally, we also have an preference order of competencies (like: use him/her in this order), Pete could be 1. welder 2. carpenter. Does this introduce new options?

A:

Thanks to Sign's suggestion we decided to go with a range of values.
The maximum value is the total number of hours available for the competencies, just counting multiple times.
The minimum value is the total number of hours from the employees who have only that one competency.
No amount of planning for other competencies can take away from that competency's hours.
See the screenshot for eamples:

We will call the minimum value the hard availability, and the range from min to max soft. We can then present the availability for each competency (per time period) as follows:

dark blue = hard
light blue = soft
red line = number of hours required
In situation a the requirement for that competency can always be fulfilled.
In situation b the requirement for that competency X can be fulfilled, if you make sure not to fully allocate people who have competency X to other competencies that they also have.
In situation c the requirement can never be fulfilled.

