Giorgio Canarella and Stephen M. Miller (both Economics and Center for Business and Economic Research) published  "Firm Size, Corporate Debt, R&D Activity, and Agency Costs: Exploring Dynamic and Non-linear Effects" in the June issue of The Journal of Economic Asymmetries. This paper empirically investigates firm-specific determinants of agency costs. We estimate dynamic agency costs models, linking debt, firm size, and R&D activity to agency costs for a panel of U.S. information and communication technology firms. We adopt the Blundell and Bond (1998) two-step system GMM technique, which explicitly accounts for persistence, endogeneity, and unobservable firm heterogeneity. Our findings imply that agency costs experience a minimum value (for debt) and a maximum value (for firm size and R&D activity) and, therefore, that agency costs are higher at both low and high levels of debt, and lower at both low and high levels of firm size and R&D activity. We find that the level of debt of the average firm in the sample falls below the level that minimizes agency costs. Our findings reveal that agency costs are dynamic in nature, mean-reverting, and persistent over time. Finally, we find a positive association between firm profitability and agency costs and a negative association between agency costs and firm growth.