What do 'acousticness' and 'valence' mean in 'audio_summary' ?

Thanks for the reply Plamere

While i need to create an app to know the song's mood, i referred from here http://developer.echonest.com/raw_tutorials/faqs/faq_03.html both correctly identify the songs but with a major different on the Energy and Valence

Identifying an MP3 file by its metadata

http://developer.echonest.com/api/v4/song/search?api_key=API_KEY&format=json&results=1&artist=The+Jackson+5&title=ABC&bucket=audio_summary

energy = "0.2688581137037661"; valence = "0.6505042994560134"; likely mood: Aggressive

Identifying an MP3 file via uploading

http://developer.echonest.com/api/v4/track/profile?api_key=API_KEY&format=json&md5=b08d7aa8e0cb628887afa53590b5fcdc&bucket=audio_summary

energy = "0.4148946356963514"; valence = "0.9282548578533839";

likely mood: Stressed

How do i know which analysis are correct ?

thanks for reading :)