Low Value for this ratio is an indicator of latching problem. Investigate the Latch Sections in AWR and Statspack report for contention on library cache and shared pool latches.
Ideally Parse Elapsed must be equal to Parse CPU, i.e., only CPU time is used for parsing. In that case the ratio is 100%. If wait time is more then the ratio will be less.
Source : https://blogs.oracle.com/myoraclediary/entry/what_is_parse_cpu_to