Abstract:
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Often in official statistics, quarterly seasonal adjustments are not the result of a direct adjustment of the quarterly series, but are an indirect adjustment formed from the aggregation of the seasonally adjusted monthly series. This method ignores a potential problem in temporal aggregation, whereby quarterly series formed from non-seasonal monthly series can exhibit seasonality; moreover, quarterly series formed from seasonal monthly series can be nonseasonal. This work examines the effect of benchmarking the seasonally adjusted monthly series to the seasonally adjusted quarterly series, utilizing adequacy of the component seasonal adjustments as an additional constraint in the benchmarking process. We focus on seasonal adjustment arising from X13ARIMA-SEATS and apply this benchmarking procedure to a component of Gross Domestic Product.
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