Context series and Indexes
For example, you might want to compare consumer behavior data in a local market to national figures to see if there are any differences, or find correlations between certain factors (do people with children buy more french fries than average). You can also use these calculations to see market share for a vendor or brand.
This chart shows Subaru new vehicle sales indexed against national Subaru sales. Numbers higher than 100 mean that the local areas are outperforming the national average for that particular make.
Context series calculations
These calculations require at least two data series: one to provide the numerator for the calculation and one for the denominator.
The table below shows the basic data for Subaru sales in the Pittsburgh market, with no context series set. The New Registrations (proportion) column gives the percentage of total calculated for each category. In other words, for the Subaru Outback, there were 1,891 registrations, which represents 16.7% of all Subaru registrations for all models. (The numbers in the New Registrations (proportion) column total 100%.)
Here is the same table with a context series defined to index Pittsburgh Subaru sales against nationwide Subaru sales.
Two new calculated values are included:
- New Registrations (%): Calculated by dividing the value for each grouping by the context series value. For example: Forester new registrations for the Pittsburgh area data series divided by the Forester new registrations nationwide data series equals the percent of Forester new registrations.
- New Registrations (Index): Calculated by dividing the proportion values for each grouping by the context series value. For example, The WRX new registrations (proportion) for Pittsburgh data series divided by the WRX new registrations (proportion) nationwide equals WRX new registrations (index)
To see these values, you must select which of your data series to use as the context series. In this example, the context series is the nationwide Subaru sales. In general, the context series is something bigger than your other data series; you typically want to compare your market to something larger.
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