If a PMA sample is not mixed with another PEA/amp, then Marquis will show the difference - no colour for PMA, purple-black for MDA
A specific methylenedioxy group indicator can also be used in place of the Marquis e.g. chromotropic acid. I know of a specific reagent test for PMA ( from literature) but it uses a poisonous gas, so until (if) a suitable replacement is found, it remains completely unsuitable for home use
Leprechaun's question relates to statistics. I saw no mention of any personal interest in obtaining MDA.
Let's keep to the topic please, you'll find many threads already dealing with reagent results. Search!