本研究探討產品市場力量(PCM_ADJ)對財務績效之影響，並檢驗租稅規避(TAXAVD)之調節作用。過去研究多聚焦單一報酬率，忽略獲利實由多重構面驅動，且少有檢驗避稅之調節效果。本研究以1987至2023年美國上市公司共36,808筆觀測值為樣本，採產業調整後Lerner Index衡量PCM_ADJ。財務績效依杜邦分析分為三構面：構面一為稅前普通股權益報酬率(PTROCE)由稅前淨營運資產報酬率(PTRNOA)與稅前財務槓桿效果(FLEV_FX)加總；構面二將PTRNOA分解為稅前淨營運利潤率(PTNOPM)與淨營運資產周轉率(NOAT)相乘；構面三則為稅前營運資產報酬率(PTROOA)與稅前營運負債槓桿效果(OLLEV_FX)相加。實證顯示，PCM_ADJ在構面一對PTRNOA(FLEV_FX)有正(負)向影響，抵銷後對PTROCE無顯著影響；構面二中，對PTNOPM之正面效果大於NOAT之負向影響，使PTRNOA為正；構面三中，對PTROOA之負面效果低於OLLEV_FX之正向影響，使PTRNOA顯著為正。然而，交乘項(PCM_ADJ × TAXAVD)在構面一對PTRNOA(FLEV_FX)有負(正)向影響，抵銷後對PTROCE無顯著影響；構面二中，對PTNOPM之負向效果大於NOAT之正面影響，使PTRNOA轉為負；構面三中，對PTROOA之正面效果低於OLLEV_FX之反向影響，使PTRNOA顯著為負。上述效果在t+1至t+3期均具一致性。

This study investigates the impact of product market power (PCM_ADJ) on financial performance and examines the moderating role of tax avoidance(TAXAVD). Prior research has predominantly focused on single return metrics, overlooking the fact that corporate profitability is driven by multiple dimensions, and few studies have examined the moderating effect of tax avoidance. Using a sample of 36,808 observations of US public companies from 1987 to 2023, this study measures PCM_ADJ using the industry-adjusted Lerner Index. Under the DuPont analysis framework, financial performance is categorized into three dimensions: Dimension 1 defines pre-tax return on common equity (PTROCE) as the sum of pre-tax return on net operating assets (PTRNOA) and pre-tax financial leverage effect (FLEV_FX); Dimension 2 decomposes PTRNOA into the product of pre-tax net operating profit margin (PTNOPM) and net operating asset turnover (NOAT); Dimension 3 breaks down PTRNOA into the sum of pre-tax return on operating assets (PTROOA) and pre-tax operating liability leverage effect (OLLEV_FX).
Empirical results indicate that for Dimension 1, PCM_ADJ has a positive (negative) impact on PTRNOA (FLEV_FX), which offset each other, yielding no significant effect on PTROCE. For Dimension 2, the positive effect on PTNOPM outweighs the negative impact on NOAT, resulting in a net positive effect on PTRNOA. For Dimension 3, the negative effect on PTROOA is lower than the positive impact of OLLEV_FX, making the overall effect on PTRNOA significantly positive. Conversely, the interaction term (PCM_ADJ × TAXAVD) exerts a negative (positive) impact on PTRNOA (FLEV_FX) in Dimension 1, offsetting any significant effect on PTROCE. In Dimension 2, the negative effect of the interaction term on PTNOPM dominates its positive impact on NOAT, turning the overall effect on PTRNOA negative. In Dimension 3, the positive effect on PTROOA is lower than the adverse impact of OLLEV_FX, resulting in a significantly negative overall effect on PTRNOA. These observed effects remain consistent from period t+1 through t+3.

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