Borsa İstanbul'da Portföy Çeşitlendirme Gücünün Zamanla Değişimi: BİST 30 Üzerine Bir Uygulama

Öz

Bu çalışmada, 2015–2025 döneminde Borsa İstanbul’da işlem gören BIST 30 şirketlerinden oluşturulan eşit ağırlıklı portföyün çeşitlendirme oranı (DR) analiz edilerek Türkiye hisse senedi piyasasında çeşitlendirme stratejisinin etkinliği incelenmiştir. 12 aylık hareketli pencere yöntemiyle hesaplanan DR değerleri, portföyün dönemsel olarak farklı çeşitlendirme güçlerine sahip olduğunu göstermektedir. Bulgular, 2018 kur krizi, 2020 COVID-19 pandemisi ve 2023 seçim süreci gibi belirsizlik dönemlerinde hisse korelasyonlarının artmasıyla DR’ın 1,3–1,5 aralığına kadar gerilediğini, buna karşın 2016–2017 ve 2024–2025 gibi istikrarlı dönemlerde 1,8–2,0 seviyelerine yükseldiğini ortaya koymuştur. Sonuçlar, çeşitlendirmenin statik değil, piyasa koşullarına duyarlı dinamik bir yapı sergilediğini göstermektedir. Türkiye sermaye piyasasında sürdürülebilir risk azaltımı için yalnızca hisse bazlı değil, farklı varlıkları da kapsayan stratejik portföy yaklaşımının benimsenmesi gerektiği sonucuna ulaşılmıştır.

Anahtar Kelimeler

• Çeşitlendirme Oranı
• Borsa İstanbul
• Portföy Riski

Time-Varying Diversification Power in Borsa İstanbul:An Application on BİST 30 Index

Abstract

This study investigates the effectiveness of diversification strategies in the Turkish stock market by analyzing the Diversification Ratio (DR) of an equally weighted BIST 30 portfolio between 2015 and 2025. Using a 12-month rolling window, the DR values reveal substantial time variation in diversification strength. The findings show that during stress periods such as the 2018 currency crisis, the COVID-19 pandemic, and the 2023 election cycle, rising stock correlations caused the DR to decline to around 1.3–1.5. In contrast, in more stable periods like 2016–2017 and 2024–2025, the DR increased to approximately 1.8–2.0, indicating a restoration of portfolio balance. These results highlight that diversification is not static but dynamically shaped by market conditions. The study concludes that sustainable risk mitigation in Turkey’s capital market requires a strategic portfolio design that integrates multiple assets rather than relying solely on stock-level diversification.

Keywords

• Diversification Ratio
• Borsa Istanbul
• Portfolio Risk

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