This question utilizes the Earned Schedule (ES) method, which is an extension of the traditional Earned Value Management (EVM) framework. While traditional EVM measures schedule variance in currency (dollars/units), Earned Schedule measures it in units of time.
According to the PMI Practice Standard for Earned Value Management and references in the PMBOK® Guide:
Identify the Variables:
Earned Schedule (ES): 16 weeks. (Note: In this specific calculation context, " ES " refers to Earned Schedule—the duration that should have been taken to achieve the current earned value—rather than " Early Start " ).
Actual Time (AT): 12 weeks.
Schedule Performance Index (SPI): 1.3 (given).
Formula for Schedule Variance (Time):
The formula for Schedule Variance in terms of time ($SV_t$) is:
$$SV_t = ES - AT$$
Substituting the given values:
$$SV_t = 16 - 12 = 4$$
Validation with SPI:
The formula for the Schedule Performance Index in terms of time ($SPI_t$) is:
$$SPI_t = ES / AT$$
Substituting the values:
$$SPI_t = 16 / 12 = 1.33...$$
This matches the provided SPI of 1.3 (rounded to one decimal place), confirming that the interpretation of the variables is correct.
Conclusion:
A positive Schedule Variance of 4 indicates that the project is 4 weeks ahead of schedule. This is consistent with an SPI greater than 1.0 (1.3), which denotes efficient schedule performance.
