Which index would you use to measure how efficiently time is being used in a project?

The Schedule Performance Index (SPI) is the correct choice for measuring how efficiently time is being used in a project. SPI is a crucial metric in project management, derived from earned value management (EVM). Its main purpose is to assess the progress of a project relative to its scheduled timeline.

SPI is calculated by dividing the earned value (the value of work actually completed) by the planned value (the value of work that was scheduled to be completed by that point in time). When the SPI is greater than 1, it indicates that the project is ahead of schedule, while an SPI less than 1 suggests that the project is behind schedule. This measure directly reflects the efficiency of time utilization in the project, helping project managers make informed decisions to steer the project back on track if necessary.

In contrast, the other indices focus on different aspects of project performance. For example, the Cost Performance Index (CPI) measures cost efficiency, the Percent Complete Index Budget (PCIB) focuses on the budget percentage completed against the total budget, and the To Complete Performance Index (TCPI) assesses the remaining cost efficiency required to complete the project within the budget. Therefore, for evaluating time efficiency specifically, the SPI is the most suitable index.