Direct and Indirect Seasonal Adjustment Approaches: An Application for GDP Series

Abstract

The seasonal adjustment of aggregated time series can be obtained indirectly through the aggregation of the main components previously seasonally adjusted or directly seasonally adjusting the aggregated series. Unfortunately, these strategies could produce quite different results. In this paper we discussed the common criteria and diagnostics used to assess the quality of a seasonal adjustment and to compare seasonal adjustment results obtained with the alternative approaches known as direct or indirect in the literature. The direct and the indirect seasonal adjustment approaches are compared on the basis of the results obtained for the seasonal adjustment of the GDP series published by the Turkish Statistical Institute. In this study we have used the quarterly data pertaining to 1998:01–2009:02 period, and have concluded that the GDP is to be adjusted using the indirect approach.

Keywords

• Direct and indirect aproach
• Seasonal adjustment
• Time series

Doğrudan ve Dolaylı Mevsim Düzeltme Yaklaşımları: GSYİH Serileri için Bir Uygulama

Abstract

Toplulaştırılmış zaman serilerinde mevsimsel düzeltme, mevsimsel düzeltilmiş ana grupların toplulaştırılması yoluyla dolaylı olarak ya da toplulaştırılmış serinin mevsimsellikten arındırılması yoluyla doğrudan elde edilebilir. Ne yazık ki bu stratejiler oldukça farklı sonuçlar üretebilir. Bu çalışmada literatürde doğrudan ve dolaylı yaklaşım olarak adlandırılan alternatif yaklaşımlarla elde edilmiş mevsimsel düzeltme sonuçlarını karşılaştırabilmek ve mevsimsel düzeltmenin kalitesini değerlendirebilmek için kullanılan genel ölçütler ve diyagnostikler tartışılmıştır. Doğrudan ve dolaylı yaklaşımla mevsimsel düzeltme yaklaşımları, Türkiye İstatistik Kurumu (TÜİK) tarafından yayımlanan Gayri Safi Yurtiçi Hasıla (GSYİH) serileriyle elde edilen mevsimsel düzeltme sonuçları temelinde karşılaştırılmıştır. 1998:01–2009:02 dönemine ait üç aylık verilerin kullanıldığı çalışmada GSYİH’nin dolaylı yaklaşımla mevsimsel düzeltilmesine karar verilmiştir.

Keywords

• Doğrudan ve dolaylı yaklaşım
• Mevsimsel düzeltme
• Zaman serileri

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