The schedule variance could be affected by many factors such as how accurate the project manager was when first establishing the schedule. It is possible that the project manager overestimates the amount of time different aspects of the project will take; in this case the team will likely be ahead of schedule and the schedule variance will be positive. On the other hand if the project manager underestimates how much time certain parts of the project will take the schedule variance may be negative because the team is behind schedule. Other factors that could affect the schedule variance are the schedules and capabilities of the team members, any requests to change the project, and an unplanned issue arising.