Behavioral Bias Analysis of Anchoring in Insider Trading: An Empirical Study Using the 52-Week High Indicator on the Ho Chi Minh Stock Exchange during the 2016-2025 Period

Abstract

This research examines the presence of anchoring bias in insider trading decisions among firms listed on the Ho Chi Minh Stock Exchange. The analysis employs monthly panel data from companies consistently included in the VN30 index over the period January 2016 to December 2025. Insider trading decisions are proxied by the Net Purchase Ratio (NPR), while the 52-week high ratio is used to capture anchoring behavior related to stock price movements. The empirical results show that the 52-week high ratio has a negative and statistically significant effect on NPR, with a coefficient of ?0.9866 and a p-value of 0.0007. This finding indicates that when stock prices approach their 52-week high levels, insiders tend to increase selling activity relative to buying. Conversely, when prices move away from this reference point, insiders are more inclined to engage in purchasing activity. The overall regression model is statistically significant, as indicated by an F-statistic probability of 0.0383, although the explanatory power remains relatively low, with an R-squared value of 0.0231. Furthermore, control variables including return, momentum, firm size, illiquidity, and turnover do not exhibit significant effects on insider trading decisions. Robustness testing confirms the consistency of the main findings. These results suggest that insider behavior is more strongly influenced by the relative position of stock prices to the 52-week high than by firm-specific characteristics. Overall, the findings provide evidence that insider trading decisions are not purely driven by private information, but are also shaped by behavioral biases, particularly anchoring to historical price levels.