  A partition statistic ` crank' gives combinatorial interpretations for
Ramanujan's famous partition congruences. In this paper, we establish an
asymptotic formula, Ramanujan type congruences, and q-series identities that
the number of partitions with even crank $M_e(n)$ minus the number of
partitions with odd crank $M_o(n)$ satisfies. For example, we show that
$M_e(5n+4)-M_o(5n+4)\equiv 0 \pmod 5.$ We also determine the exact values of
$M_e(n)-M_o(n)$ in case of partitions into distinct parts, which are at most
two and zero for infinitely many $n$.
