Evaluación de los impactos ambientales en el proceso de producción

Once the status has been determined for the project, i.e., the PV, EV, and AC values have been determined for the current period for each work package, what does the data mean and how is it presented in a useful way?

Several earned value calculations allow the project manager to evaluate both schedule performance and cost performance.

A variance is a difference between actual project results and planned or expected results. A positive variance means that a project is ahead of schedule or under budget, while a negative variance indicates that a project is behind schedule or over budget.

An index is a measure used to assess the magnitude of any project variances that do occur. For indices, a value greater than 1.00 is better than planned efficiency, while a value less than 1.00 indicates that efficiency is less than planned.

EVMS Schedule Formulas

• Schedule variance (SV) = EV - PV

• Schedule performance index (SPI) = EV/PV

• Preferred state: SV is positive, and SPI is greater than 1.00

o This means that the earned value is greater than the planned value. More work has been earned than planned, so the project is on or ahead of schedule.

EVMS Cost Formulas

• Cost variance (CV) = EV - AC

• Cost performance index (CPI) = EV/AC

• Preferred state: CV is positive, and CPI is greater than 1.00

o This means that the earned value is more than the actual cost. More value has been earned than the actual cost expended, so the project is on or under budget.

Example of EV Components

The example below illustrates these values at a time of status measurement.

EV Component Example

In this example, the project is to build five prefab sections of a house for a total project budget of $500 (BAC). Recall that at the end of the project, the final PV equals the budget

at completion (BAC). The task now is to compute the PV at this point in time.

It was expected that $300 worth of tasks were to be completed (PV). In reality, only $200 worth has been completed (EV); but the accounting system collected expenses of $400 (AC) on the project.

EVMS Example

The following EVMS example uses the earned value formulas to calculate the variances and indices. • PV = 300 • EV = 200 • AC = 400 • SV = EV-PV = 200 - 300 = (100) • SPI = EV/PV = 200/300 = 0.67 • CV = EV-AC = 200 - 400 = (200) • CPI = EV/AC = 200/400 = 0.50

The calculations in this example indicate that the project is behind schedule and over budget, with poor schedule and cost efficiency ratios.

• The SPI of 0.67 indicates that the project has accomplished only 67% of the work it was scheduled to accomplish by the status date.

• The CPI of 0.50 indicates that for every $1.00 spent on the project, only $.50 worth of work has been completed.

EVMS Diagram

The results of the EVM analysis are usually graphed to provide a powerful status report for the project. Such a diagram can be tracked at the total project level, and also for each control account. Project management software tools can help present this information. The EVMS data in the diagram below depicts the values over time for the three key parameters, PV, EV, and AC. The status reporting period during which these parameters were calculated is shown via the Update Now vertical line. At that point in time, the schedule and cost variances are depicted on the graph as the difference between EV and PV (schedule variance) and between EV and AC (cost variance).

Another powerful feature of the diagram is its ability to show the trends in performance from one reporting period to the next. An experienced eye can read these charts quickly and draw conclusions about the project's performance, past, current, and future.

The EVMS diagram also illustrates how EV calculations provide more insight into the overall project health than straight comparisons between the original baselines and actual costs.

If the actual costs are less than the original cost baseline, it may appear that the project is under-spending. However, by comparing EV to AC, a project manager realizes that, in reality, the project is paying too much for the work actually performed.

By comparing EV to PV, it is apparent that less work was accomplished than planned at the point of determining the project's status; therefore, the project is behind schedule. The key to understanding EV is that the cost or schedule is always compared to the value of the work performed-EV or the earned value.

Forecasting Costs

When the project manager knows the current project cost, he can also predict where the project is going using EV. This requires calculating at-completion and to-completion costs. There are several terms to define in learning and applying these calculations.

Estimating the At-Completion Project Cost (Terms)

Budget at Completion (BAC)

• Total cumulative PV at completion of a schedule activity, work package, control account, or other project component

o When applied to the entire project, BAC represents the total budget of the project, not including management reserve

o At project completion, BAC will equal PV

Estimate at Completion (EAC) - also called Latest Revised Estimate (LRE)

• Estimate, or forecast, of the most likely total value based on project performance and risk quantification

o EAC can be greater than or less than BAC

Estimating the To-Completion Project Cost (Terms)

Estimate to Complete (ETC)

• Estimate for completing the remaining work for a schedule activity, work package, control account, or other project component

o ETC is the difference between EAC and actual costs to date

Estimating the At-Completion Costs