Preferential trade agreements spur discriminatory anti-dumping practices:

“In this paper we empirically explore the possibility of additional discrimination via PTAs by focusing on the extent to which PTAs alter the pattern of antidumping (AD) activity… AD provisions in PTAs have decreased the number of intra-PTA AD cases by 33-55% and increased the number of AD actions against non-PTA members by 10-30%… PTAs without AD language do not experience any change in AD activity whereas PTAs with AD rules are characterized by protection reduction and protection diversion.”

Just as it’s difficult to assess the net benefits of trade creation minus trade diversion, it’s likely tough to discern the net benefit of PTAs’ AD clauses in terms of protection reduction minus protection diversion.