How do I Calculate Seasonality?

by Andrea Stein; Updated September 26, 2017
A run sequence plot calculates seasonality, or fluctuations that occur in a data series.

Seasonality refers to periodic fluctuations exhibited by time series, or a statistical sequence of data points measured at uniform time intervals. Seasonality can be calculated via a run sequence plot.

Run Sequence Plot

A run sequence plot refers to a graph used to display observed data in a time series, and it typically represents an aspect of the performance or output of a business-related process. The run sequence plot displays data samples taken over a specific period of time. An example of run sequence plot data would be the temperature of a dish washing machine each time it is run, where time would be represented by the (Y) vertical axis, and the amount of water used to run the machine during a cycle represented by the horizontal (X) axis.

Anomalies

Run sequence plot charts are analyzed to detect anomalies, or unusual measurements, that occur during a time series. Factors involved in analyzing anomalies include abnormally long series of consecutive decreases or increases in data, and the total amount of such series in a data set.

Seasonal Subseries Plot

The seasonal subseries plot may be used after a run sequence plot is constructed to detect seasonal differences between group patterns and within group patterns. Season subseries plots use a horizontal axis to display time ordered by month. The vertical axis represents a time variable, or values directly dependent on time.

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