In parliamentary systems, executives play a major legislative role: they draft and propose legislation, and build the necessary coalition to ensure that a given bill will become law. Other parliamentary groups are often seen as residual, having very little influence on the policy making process. However, some parliamentary groups might be more effective than others at inserting their policy proposals into enacted legislation. Due to data and methodological limitations, large-N and systematic studies of the conditions under which parliamentary groups are successful at influencing legislation are extremely rare, leaving crucial questions about who and why has power at influencing legislation unanswered. To what extent do parliaments reverse executive proposals? What parliamentary groups are more efficient in performing this task? In order to answer these questions, first, we compare executive bills proposals as they enter the legislative process with the final text of laws using text reuse methods. Next, we identify the parliamentary group responsible for the different amendments and calculate the amendments’ efficiency rate for each group. The theoretical framework explores causality considering variations in the type of government, ideological distance among parties, political polarization and issue jurisdiction. The analysis relies on a database containing all the executive bills introduced into the Spanish Parliament from 1996 to present.
