  We study the complexity of deciding whether there is a tie in a given
approval-based multiwinner election, as well as the complexity of counting tied
winning committees. We consider a family of Thiele rules, their greedy
variants, Phragmen's sequential rule, and Method of Equal Shares. For most
cases, our problems are computationally hard, but for sequential rules we find
an FPT algorithm for discovering ties (parameterized by the committee size). We
also show experimentally that in elections of moderate size ties are quite
frequent.
