Assign uncertainty to productivity levels in the project

The time it takes to complete a task within a project is dependent on the actual amount of work involved (like lines of code to be written, number of welds, volume of concrete needed, etc.), taken care of in Step 2, and on the productivity level (the rate with which one can complete the work). In this section, we focus on the productivity.

There are three steps to incorporating uncertainty about productivity:

  1. Define productivity risk factors

  2. Create work type categories with different mixes of productivity risk factors

  3. Apply these work type categories to individual tasks in the schedule

 

1: Defining productivity risk factors

Many factors affect how efficiently a task gets completed, and therefore how long it takes. These factors can be organizational (level of communication, coordination, etc.), human (level of competence, motivation), equipment (throughput level, reliability), etc. In this section we define the productivity factors that can have an effect on various parts of the project, e.g. ‘welding contractor expertise’, ‘cooperation with client’, etc. We then map them to different work type categories in the next section.

Click the Productivity Risk Factors icon in the Task Overview tab:

This opens a dialog:

In this example, a number of Productivity Risk Factors have been created. You can add and delete new PRFs by clicking the appropriate buttons. The data required are:

  • A description of the Productivity Risk Factor (only used in this window to assist understanding)

  • A short title (which will appear in some results charts)

  • The probability of occurrence (often set to 100%, but sometimes less – for example, 30% has been entered in the above table for ‘Poor site management’ reflecting that there is only a 30% chance that this would be an issue at all)

  • The minimum, most likely and maximum percentage effect on the time taken to complete the work. For example, unskilled steel workers in the above table would have the effect of increasing the time taken to complete a task between 0% and 30%, most likely 10%.

Note that we must always have Minimum < Most Likely < Maximum (an error message will show if this is not the case), and that it is also possible to have negative values if you think that a Productivity Risk Factor might reduce the amount of time required to complete a task.

The entries within the table can be reordered by clicking the headers in each column.

If a Productivity Risk Factor is deleted from the model, it will not change the ID codes of the other factors. This helps ensure that one can readily identify which Productivity Risk Factors are retained in the model from one version to another.

Click Save after making any changes to the Productivity Risk Factors.

2: Defining work type categories

Work Type Categories allow you to group similar activities for which the productivity rate is influenced by the same productivity risk factors. Typically, these Work Type Categories will involve the same or similar team of people.

Click the Work Type Categories icon in the Task Overview tab:

This will open the following dialog:

If, during import of the project file, one has opted to include a particular activity code field to represent the Work Type Categories, they will be listed in the table. In this example, a number of Work Type Categories have been created. You can add and delete new Work Type Categories by clicking the appropriate buttons. The data required are:

  • A name for the Work Type Category

  • [Optionally] A color to use within the task table

  • The fraction of the work that would be affected by each Productivity Risk Factor

In the example above, for the Work Type Category ‘Roofing’, the Productivity Risk Factors ‘Steel skill’ and ‘Client indecision ‘affect 0% of the work, , but ‘Building’, ‘Design’, ‘Teamwork’, ‘Site management’ and ‘Roof design’ can affect about 20%, 30%, 40%, 50%, and 100% of the work respectively. The higher the fraction (closer to 100%) the darker red the label.

Productivity rates are a major cause of risk in a project, particularly because they produce correlation between task completion times. Despite being critical for the proper evaluation of schedule uncertainty, the modelling of correlation was considered essentially impractical until the emergence of Tamara. This article explains more about correlation and its effect on project schedule risk.

The use of different mixes of Productivity Risk Factors for various categories of work makes it very quick and easy to incorporate the uncertainty driven by common factors in an intuitive way.

On the left of the table a color key shows the color that is used to indicate which Work Type Category is used for a particular task. To change the color, click on the colored box and select a new color from the dropdown box.

The entries within the table can be reordered by clicking the headers in each column. If a Work Type Category is deleted from the model, it will not change the ID codes of the other Work Type Categories. This helps ensure that one can readily identify which Work Type Categories are retained in the model from one version to another.

Click Save after making any changes to the PRFs. A Work Type Category set is dependent on the PRFs that it uses. If the PRF set in current use does not include all the Productivity Risk Factors that the Work Type Category expects to see, Tamara will work with the Productivity Risk Factors remaining.

3: Applying work type categories to individual tasks

 

Applying a Work Type Category category is done in the Main View, under the Task Overview tab. One simply selects the appropriate Work Type Category description in the Category column as shown below. Selecting a Work Type Category for a parent task will apply that Work Type Category to all child tasks, which can then be altered individually. Ordering by Work Breakdown Structure (WBS), Cost Breakdown Structure (CBS) or any other grouping that was defined in the original model will usually make this task a lot easier.

Note that the color-coding shown in the Work Type Categories table is applied here.

 

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