Thesis Defense – Ömer Faruk Karaahmetoğlu

“Firm Size, Growth, and Growth Volatility: Evidence from the Universe of Registered Turkish Firms”

Thesis Defence – Ömer Faruk Karaahmetoğlu

Asst. Prof. Dr. Han Özsöylev– Advisor

Date: 23.07.2026

Time: 11:30

Location: Özyeğin University Altunizade Campus – Meeting Room 301

Thesis Committee:

Asst. Prof. Dr. Han Özsöylev, Özyeğin University

Asst. Prof. Dr. Yusuf Kulu, Özyeğin University

Prof. Dr. Mehmet Yorukoglu, Koc University

Abstract:

We study firm-level growth volatility on the universe of registered Turkish firms, observed annually from 2009 to 2024 with each firm's supplier and customer linkages. The canonical network prediction is that broader production networks dampen idiosyncratic volatility symmetrically across upstream and downstream linkages. We show, empirically and in a structural model of the firm's supply network as a financially constrained choice, that this symmetry holds only as a frictionless benchmark: customer-sector breadth dampens firmlevel volatility while supplier-sector breadth amplifies it. The asymmetry has a simple source: inputs are complementary in production, so an unbuffered supplier's disruption can halt output and cannot be averaged away, whereas customers are substitutable in revenue, so a weak customer sector is absorbed by the rest. We propose and find support for a statedependent mechanism: supplier-sector breadth is expanded reactively after negative shocks and proves fragile when the firm's own sector weakens, raising volatility in downturns and lowering it in booms, while scale shelters larger firms from sector-overheating volatility. The customer-side dampening confirms existing customer-concentration findings; the supplierside amplification, and the mechanism explaining it, are new.

Keywords: firm dynamics, production networks, growth volatility, financial constraints, emerging markets

Bio:       

Ömer Faruk Karaahmetoğlu, having graduated from the Department of Economics at TOBB University of Economics and Technology in 2021, currently works at the Central Bank of the Republic of Turkey (TCMB) as an  Assistant Specialist.