In the EVM concept, a SPI greater than 1 indicates:

The Schedule Performance Index (SPI) is a key metric in Earned Value Management (EVM) used to measure schedule efficiency. It is calculated by the formula SPI = EV / PV, where EV is the Earned Value (the value of work actually completed) and PV is the Planned Value (the value of work scheduled to be completed). An SPI value greater than 1 indicates that the project has completed more work than was planned for the period (EV > PV). This signifies that the project is ahead of schedule. Therefore, the team has used less than the planned time (100% or less) to accomplish the scheduled work, demonstrating favorable schedule performance.

A. This describes the Cost Performance Index (CPI), not SPI. A CPI greater than 1 indicates the project is under budget.
B. This describes poor cost performance (CPI < 1), where the project is over budget, not ahead of schedule.
D. This describes a project that is behind schedule, which would be indicated by an SPI less than 1.

1. Project Management Institute. (2021). A Guide to the Project Management Body of Knowledge (PMBOK® Guide) (7th ed.). Section 2.7.3, Performance Measurement. The guide defines SPI as EV/PV and states, "An SPI value greater than 1.0 indicates more work was completed than was planned."

2. Fleming, Q. W., & Koppelman, J. M. (2016). Earned Value Project Management (4th ed.). Project Management Institute. Chapter 6, "Schedule Analysis," pp. 51-52. This text explains that an SPI greater than 1.0 is a favorable condition, indicating the project is ahead of its baseline schedule.

3. MIT OpenCourseWare. (2012). 16.852J / ESD.352J Integrating the Lean Enterprise, Fall 2005. Lecture 11: Program Management & Control. Slide 21, "Cost/Schedule Status." The material defines SPI = BCWP/BCWS (Budgeted Cost of Work Performed / Budgeted Cost of Work Scheduled, an alternative notation for EV/PV) and notes that SPI > 1 means the project is ahead of schedule.