Measuring the outcome of interest group lobbying constitutes one of the greatest challenges to interest group scholars. This paper contributes to this theoretical and methodological debate by analysing one specific formal channel of influence, namely letters sent from interest groups to the Dutch parliament. More specifically, we analyse the conditions under which such letters receive three types of reactions, which represent different types of agenda-setting influence. We distinguish between whether a letter is taken note of, being added to the agenda for further discussion or results in a profound reaction, including new meetings, questions to parliamentarians or the letter being forwarded to ministers. Our analysis is conducted by linking information about the reactions to the 2732 letters sent by 974 interest groups to Dutch parliamentary committees during 2011 with background information about the groups from a survey of Dutch interest representatives. To assess which factors explain the reactions letters receive we employ multinomial logistic regression. Our preliminary findings suggest that business groups have a higher chance of getting their letters on the parliamentary agenda rather than simply being taken note of. However, when it comes obtaining profound reactions business groups are no longer advantaged. Moreover, we see that letters containing “information” or “comments and reactions” have a higher chance of getting through to the agenda than requests for action. Instead, such requests are more likely to result in new meetings, questions to parliamentarians or being forwarded to ministers than letters providing information. These preliminary results provide strong grounds for building analysis designs sensitive to the fact that the causal factors that explain different types of influence vary. In this way, they suggest that future research on the outcome of interest group lobbying needs to emphasize differences, not only between channels and venues, but also between different types of influence.
