We discuss Andrews' recent statistics on integer partitions, the upper odd, upper even, lower odd, and lower even parity indexes, relating to how the parts of an integer partition change in parity. First, we will define the statistics, and give combinatorial proofs (independently found by Kursungoz) of Andrews' generating functions of the statistics over all partitions and over partitions with distinct parts. Next, we will define overpartitions (also known as MacMahon diagrams), a generalization of the integer partitions, and give original generating functions for the parity indexes over overpartitions, which generalize Andrews' generating functions. Finally, we will discuss the connections between the parity indexes and the famous Rogers-Ramanujan identities.