## 2 Review of Previous Studies
### Dynamic Shock Theory  
Dynamic Shock Theory does not refer a theory defined in specific terms, but it provides an important basis for various prior studies related to the dynamic analysis of uncertain economic shocks [54]. In particular, VARM and IRF confirmed that economic shocks are the most suitable methods for analyzing the dynamic impact of economic variables as impact factors according to time series continuous flow. For example, [PERSON] [55] proposed a VARM to understand the effects of exogenous shocks on various economic variables, which dynamically explains how economic shocks propagate within the system and how they affect other variables. The VARM based on dynamic impact theory models the interaction between various variables in the economic system and analyzes the impact of a shock on a specific variable on another variable over time. IRF is a very useful interpretation method for visualizing these dynamic effects to analyze how economic shocks are transmitted and absorbed into other variables [56]. The VARM and IRF approaches can be applied to industries such as logistics companies that are affected by exogenous factors exposed to the global market. This is because logistics companies' financial variables, such as profitability and stock prices, change dynamically due to external shocks, which is a useful interpretation framework for interpreting various exogenous factors as the impact on logistics companies over time [57].  
In reality, applying this theoretical background through the example of shipping companies can be used for events such as sudden fluctuations in charter rates, rising fuel costs, and the COVID-19 pandemic as major exogenous shocks. First, fluctuations in charter rates occur due to the supply-demand imbalance in the shipping market, which can have a positive or negative impact on a company's short-term profitability. Using the IRF to dynamically analyze the impact of charter shocks on shipping companies' financial performance in this negative impact scenario, it is possible to visually represent a process in which these shocks increase profits in the short term but can weigh on the cost structure in the long term.  
Second, the surge in ship fuel costs has a significant cost shock to shipping companies. This is because changes in international oil prices directly affect the profitability of shipping companies. These cost shocks can be dynamically analyzed through the VARM, and the impact of rising ship fuel costs on the financial position and profitability of shipping companies can be explained over time. As a result, shipping companies will come up with various countermeasures to reduce costs and secure sustainability, such as improving the efficiency of ship fuel and converting to alternative ship fuels.  
Third, the COVID-19 pandemic caused complex exogenous shocks to shipping companies. This caused disruptions in the global logistics supply network, port closures, and delays in ship operations, which greatly damaged the profitability of shipping companies but, at the same time, served as an opportunity to create new opportunities. Using the VARM and the IRF, it is possible to analyze the dynamic impact of the complex impact of the COVID-19 pandemic on the performance of shipping companies and visually grasp the process of companies adapting and recovering from the pandemic shock.