  In approval-based committee (ABC) voting, the goal is to choose a subset of
predefined size of the candidates based on the voters' approval preferences
over the candidates. While this problem has attracted significant attention in
recent years, the incentives for voters to participate in an election for a
given ABC voting rule have been neglected so far. This paper is thus the first
to explicitly study this property, typically called participation, for ABC
voting rules. In particular, we show that all ABC scoring rules even satisfy
group participation, whereas most sequential rules severely fail participation.
We furthermore explore several escape routes to the impossibility for
sequential ABC voting rules: we prove for many sequential rules that (i) they
satisfy participation on laminar profiles, (ii) voters who approve none of the
elected candidates cannot benefit by abstaining, and (iii) it is NP-hard for a
voter to decide whether she benefits from abstaining.
