Impact in Agriculture

Time Series Analysis of Potato Prices in Türkiye: Forecasting with the Holt–Winters Exponential Smoothing Model

Mutlu Bulut ¹

Abstract

This study examines the behavior of monthly potato producer prices in Türkiye and evaluates the forecasting performance of Holt–Winters exponential smoothing models. Using publicly available data from 2015 to 2024, the analysis reveals a clear structural shift in price levels after 2020, characterized by a strong upward trend, increased volatility, and more pronounced seasonal fluctuations. To model these dynamics, both additive and multiplicative Holt–Winters specifications were estimated using a training period of 2015–2021 and validated against out-of-sample observations from 2022–2024. The results show that the multiplicative model outperforms the additive version across all forecast accuracy measures, indicating that seasonal variations scale with the level of the series. Visual comparisons further confirm that the multiplicative approach provides a closer fit to the observed price movements, particularly during periods of elevated market volatility. A twelve-month-ahead forecast for 2025 suggests that prices are likely to remain high but relatively stable. The findings demonstrate that the Holt–Winters method offers a practical and transparent framework for short-term forecasting in agricultural markets, while highlighting the challenges posed by structural changes and sudden shocks. The study contributes to the literature by providing an updated assessment of price dynamics in Türkiye’s potato market and by identifying a suitable forecasting approach for commodities with strong seasonal patterns.

Keywords: Potato Prices; Time Series Analysis; Holt–Winters Exponential Smoothing; Seasonal Forecasting

Acknowledgment

Generative AI tools (ChatGPT) were used exclusively for language editing, organization of text, and assistance in structuring the analysis. All statistical procedures, data interpretation, and conclusions were conducted and reviewed by the author. The author takes full responsibility for the accuracy and integrity of the final manuscript.

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