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Thursday, March 5, 2015

Granger Causality & Seasonal Adjustment

One decision that we often have to make when modelling with time-series data is whether to use "seasonally adjusted" data, or the original (unadjusted) data. In some cases the decision is effectively made for us - only the seasonally adjusted data are published. This arises, for example, with some U.S. macroeconomic data, and it can be a bit of a pain.

For some previous comments on this, see here.

However, suppose that we have a choice - original data, or data that have been seasonally adjusted by some filtering method (e.g., the Census X-11/12/13 filter) - and we're interested in testing for Granger causality. Is there any evidence in favour of using one version of the data or the other?

Well, yes, there is. Let's take a look at it.