  Confirmation bias and peer pressure both have substantial impacts on the
formation of collective decisions. Nevertheless, few attempts have been made to
study how the interplay between these two mechanisms affects public opinion
evolution. Here we propose an agent-based model of opinion dynamics which
incorporates the conjugate effect of confirmation bias (characterized by the
population identity scope and individual stubbornness) and peer pressure
(described by a susceptibility threshold). We show that the number of opinion
fragments first increases and then decreases to one as population identity
scope becomes larger in a homogeneous population. Further, in heterogeneous
situations, we find that even a small fraction of impressionable individuals
who are sensitive to peer pressure could help eliminate public polarization
when population identity scope is relatively large. Intriguingly, we highlight
the emergence of 'impressionable moderates' who are easily influenced, hold
wavering opinions, and are of vital significance in competitive campaigns.
