If you want to sum values across few series, there are two main ways to achieve this:
1. Formula language
You can sum multiple series by typing a simple expression with the “+” sign.
It will add up only common part for all series.
2. Cross Section analysis
Use the Cross section analysis to calculate a sum across series. This is a good option if you want to sum up a large number of series, because you can easily include many series at once.
Cross section Sum option works the same as adding series using "+" sign. However, it is worth to note that outcome will be different if you untick Include only observation where there are values for all series option. Then Cross section will add values in all available points in time.
In case you want to sum values of one series Sum(series) formula will be helpful. It only sums values across one series, output would be one value repeated for all observations, as it returns the sum of all numbers in the series.
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