Social media news sharing has become a central subject of scholarly research in communication studies. To test current theories, it is of the utmost importance to estimate meaningful parameters of news sharing behavior from observational data. In this article, we retrieve measures of ideological congruence, issue salience, and media reputation to explain news sharing in social media. We describe how the proposed statistical model connects to different strands of the news sharing literature. We then exemplify the usefulness of the model with an analysis of the relationship between ideological congruence and issue salience. Results show that if ideology and salience correlate with each other, the preferences of ideologues (i.e. users that give higher weight to ideological congruence) will be overrepresented in observational data. This will result in heightened perceptions of polarization. We test the performance of the model using data from Brazil, Argentina, and the US.