Did Turkish Banks Sustain High Margins? Hidden Markov Evidence from the 2007– 2011 Investigation Window

Abstract

This paper examines whether the Turkish Competition Authority’s 2007–2011 investigation window coincided with persistently high loan-deposit margins in Turkish banking. We use weekly data from the Central Bank of the Republic of Türkiye for 2 June 2006–28 March 2025. Consumer and commercial margins are constructed as the relevant loan rate minus the aggregate Turkish-lira deposit rate. We estimate separate two- and three-state Gaussian hidden Markov models for each margin. To reduce the risk of local optima, we standardize each series, use multiple deterministic and randomized starting values, and order regimes by their estimated mean margins. The results do not indicate a sustained high-margin regime during the investigation window. Mean margins are lower inside the window than outside it. In the preferred three-state models, the high state accounts for only 1.9% of consumermargin weeks and 4.7% of commercial-margin weeks. The analysis is a descriptive economic screen and does not determine the existence, scope, participants, or legal characterization of any infringement. It does not corroborate the narrower aggregate outcome hypothesis that the full investigation window was characterized by continuous, cross-market margin elevation.

Keywords

• Hidden Markov Model
• Collusion Screening
• Banking competition
• Interest Margins
• Turkish Competition Authority
• Regime Switching

Supporting Institution

The author did not receive support from any organization for the submitted work.

Türk Bankaları Yüksek Marjları Sürdürdü mü? 2007–2011 Soruşturma Dönemine İlişkin Saklı Markov Bulguları

Abstract

Bu çalışma, Türkiye Rekabet Kurumu'nun 2007–2011 soruşturma döneminin Türk bankacılığında sürekli biçimde yüksek kredi–mevduat marjlarıyla örtüşüp örtüşmediğini incelemektedir. Türkiye Cumhuriyet Merkez Bankası'nın 2 Haziran 2006–28 Mart 2025 dönemine ait haftalık verileri kullanılmaktadır. Tüketici ve ticari marjlar, ilgili kredi faizinden toplulaştırılmış Türk lirası mevduat faizinin çıkarılmasıyla oluşturulmaktadır. Her marj için ayrı iki ve üç durumlu Gauss saklı Markov modelleri tahmin edilmektedir. Yerel optimum riskini azaltmak amacıyla seriler standartlaştırılmakta, çok sayıda belirlenimci ve rastgele başlangıç değeri kullanılmakta ve rejimler tahmin edilen ortalama marjlarına göre sıralanmaktadır. Bulgular, soruşturma döneminde sürekli bir yüksek marj rejimine işaret etmemektedir. Ortalama marjlar, dönem içinde dönem dışına kıyasla daha düşüktür. Tercih edilen üç durumlu modellerde yüksek durum, tüketici marjı haftalarının yalnızca %1,9'unu ve ticari marj haftalarının %4,7'sini oluşturmaktadır. Analiz betimleyici bir iktisadi tarama olup herhangi bir ihlalin varlığını, kapsamını, katılımcılarını veya hukuki niteliğini belirlemez. Bulgular, soruşturma döneminin bütününün sürekli ve piyasalar arası bir marj yükselmesiyle nitelendiğine dair dar toplulaştırılmış sonuç hipotezini desteklememektedir.

Keywords

• saklı Markov Modeli
• kartel taraması
• bankacılıkta rekabet
• faiz marjları
• Rekabet Kurumu

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