time series　

time series　时间数列　

Values taken by a variable over time（such as daily sales revenue，weekly orders，monthly overheads or yearly income）and tabulated or plotted as chronologically ordered numbers or data points.To yield valid statistical inferences，these values must be repeatedly measured often over a four to five year period.Time series consist of four components，seasonal variations that repeat over a specific period such as a day，week，month，season；trend variations that move up or down in a reasonably predictable pattern；cyclical variations that correspond with business or economic“boom-bust”cycles or follow their own peculiar cycles and random variations that do not fall under any of the above three classifications.