Time Series Analysis for Stock Price Forecasting: Evidence from Kansai Design Co., Ltd. (603458)

Stock price forecasting plays a critical role in investment decision-making, particularly in emerging sectors such as engineering consulting. Kansai Design Co., Ltd. (603458), a state-controlled listed firm, has drawn growing attention with China's ongoing infrastructure expansion. However, few studies have systematically examined its stock price dynamics using rigorous time series methods, leaving a gap in empirical evidence for short-term predictability. This study employs time series analysis to investigate the company's daily stock prices from October 10, 2022, to September 28, 2023. Following the established paradigm of stationarity testing, model identification, parameter estimation, and diagnostic checking, an Augmented Dickey-Fuller test confirmed series stationarity. Autocorrelation and partial autocorrelation analyses indicated the suitability of an autoregressive model. Comparative evaluation of AR (1), AR (2), and AR (3) models demonstrated that AR (1) provided the best fit, consistent with Occam's Razor. Residual diagnostics verified white noise properties, while predictive performance metrics showed high accuracy (RMSE = 0.0519; MAPE = 0.414%). The AR (1) model closely tracked actual prices, with errors mainly driven by random fluctuations rather than systematic bias. These findings highlight the short-term continuity of stock prices and demonstrate the model's practical value as a decision-support tool. The study contributes methodological insights and offers investors evidence-based guidance while emphasizing the importance of integrating quantitative models with fundamental market analysis.