Performance deviation parameters and sub-parameters

Before commencing the ‘on-site’ phase of construction, a planning ‘baseline’ is usually developed from the project program. This consists of predicted durations and costings for tasks in the project lifecycle. A project baseline builds upon the previous experience of construction project

managers to create a plan that represents their expectations for the project. As construction progresses, the baseline is used for each project task, to compare the original plan for the project with its actual course. It is

possible to see which tasks started earlier or later than planned, exceeded their original budget, took longer than planned, and so on.

There are actually three types of planning values: baseline (predictive and pre-project), estimated (revisions to baseline values made during a project) and actual. Before a project starts, all of its values are of the type ‘baseline’. After commencement, uncertainty is slowly replaced with certainty. Values before any given project time ‘T are gradually transformed into the type ‘actual’. Values after project time ‘T move towards ‘estimated’, as the baseline is revised. It is almost necessary to suggest that all baseline values become estimated values, at project commencement. Eventually, all values become actual values. Project progress reports are usually based on either actual and estimated data or just actual data. Reports combining actual and estimated data may be termed ‘at completion’. They predict the outcome at completion of the project, based on current status. Reports using only actual data may be called ‘to date’, as they only consider progress up to project time ‘T . Project planning is essentially concerned with project data concerning ‘time’ and ‘cost’. Reports generated for either of these parameters may be of the type ‘at completion’ or ‘to date’.

Time and cost may be categorised as performance deviation

parameters’. That is to say, they can be used to measure deviations from the project baseline. These can be seen on the three-dimensional framework for construction planning performance, proposed in the last section.

Further to this, there are a variety of measurements that can be made for each of the deviation parameters. Most of these correspond to elements of the standard Earned Value Analysis diagram (see Section 4.3 and Figure 4.1).

The most frequently used and relevant of these ’deviation sub­ parameters' are-

Cost deviation parameter/reporting to date;

• COST VARIANCE, units £s. At this point in the project, is completed work on this task over budget (see Cost Variance in Figure 4.1)?

• SCHEDULE VARIANCE, units £s. At this point in the project, how are we doing on this task compared with the estimated spend (see Schedule Variance in Figure 4.1)?

Cost deviation parameter / reporting at completion:

• VARIANCE AT COMPLETION, units £s. At the end of the project, what is the difference predicted to be between the current estimate of the total cost for this task and the original estimate (shown as Forecast Cost Overrun in Figure 4.1)?

Time deviation parameter/ reporting to date:

• SCHEDULE SLIP, units days. At this point in the project, what is the difference between the elapsed time estimated and the actual elapsed time (shown as Schedule Variance -time- in Figure 4.1)?

Time deviation parameter/ reporting at completion;

• DURATION VARIANCE, units days. In Earned Value Analysis

terminology, this is sometimes called Projected Program Delay. At the end of the project, what is the difference predicted to be between the current estimate of the total time to complete this task and the original estimate (shown as Forecast Project Time Slip in Figure 4.1)?

• WORK VARIANCE, units hours. At the end of the project, what is the difference predicted to be between the current estimate of total number of person hours to complete this task and the original estimate (not shown in Figure 4.1)?

It should be noted that a third deviation parameter might be described as ‘conformance’ or ‘quality’. Objective measurement of this parameter is not a simple matter. As yet, conformance has not been implemented in the

Procession software tool. One possible approach to measuring quality might be a quantitative assessment of snags’ within a given time period. Whilst recognising its importance to construction projects, it has been decided that this is beyond the scope of this research (see Section 10.3 Implementing ‘quality’ as a deviation parameter).

Figure 5.3 presents the 3D framework with the addition of the deviation sub-parameters.

Deviation Level (Y )

Example data surface \ Tasks (Z ) Deviation Parameters ( X ) Conformance Cost — (variance) Tune (slippage) 1. Cost Variance 2. Schedule Variance 3. Variance At Completion 4. Schedule Slip 5. Contour Percent Variance Duration Variance Work Vanance

Figure 5.3 A 3D framework for measuring construction planning performance (including deviation sub-parameters), source: author.

5.4 Chapter summary and contextualisation

In Chapter 4, Earned Value Analysis was introduced as one of the main systems for 2D project performance reporting (see Section 4.3). This chapter has proposed a 3D morphological framework for construction planning. The author has described this in more detail elsewhere (North 2000b, pp.577-582).

The 3D framework has the following dimensions: X= deviation parameters, Y= deviation level and Z= tasks. The X dimension (deviation parameters) has the following deviation sub-parameters: Cost Variance, Schedule Variance, Variance At Completion, Schedule Slip and Duration Variance. It should be noted that the performance deviation sub-parameters (explained in Section 5.3) are derived from standard measurements utilised for Earned Value Analysis (see Section 4.3). It should be noted that Contour

Percent Variance is a non-standard sub-parameter, developed by the Researcher and not relevant to this thesis. In the next chapter, the 3D framework is implemented as a data surface in the Procession software tool.