Which metric is used to measure the efficiency of project costs against work performed?

The Cost Performance Index (CPI) is a key metric used in project management to evaluate the efficiency of a project's financial performance. Specifically, CPI measures the ratio of earned value (the value of work actually completed) to actual costs incurred for that work.

A CPI greater than 1 indicates that the project is under budget, meaning that more value is being earned per dollar spent. Conversely, a CPI less than 1 suggests that the project is over budget, as less value is being realized for each dollar spent. This metric is crucial for assessing how well the project is managing costs relative to the work completed, thereby providing insight into whether corrective actions need to be taken to ensure the project remains on track financially.

In contrast, other metrics such as Budget at Completion (BAC) and Estimate at Completion (EAC) pertain more to overall budgeted and projected costs rather than the efficiency of spending against work completed. The Schedule Performance Index (SPI), while also a performance metric, specifically measures schedule efficiency rather than cost efficiency. Thus, CPI is the appropriate choice for measuring cost efficiency relative to work performed.