Seasonal factors refl ect the variations that repeat every
year to the same extent, e.g., holiday effects, weather
fl uctuations representative of the season, and so on. A
monthly seasonal factor represents the impact that a
particular month of the year has on a particular measure
relative to what that measure would be if the seasonal
infl uence were removed – or “deseasonalized.”
In the case of congested hours, the seasonal factor
represents how many more (a positive number) or fewer
(a negative number) hours would be expected due to
the month being observed. A seasonal factor near zero
indicates little deviation from the underlying trend.