erratic vs patchy

erratic

adj
  • Unsteady, random; prone to unexpected changes; not consistent. 

  • Deviating from normal opinions or actions; eccentric; odd. 

noun
  • A rock moved from one location to another, usually by a glacier. 

  • Anything that has erratic characteristics. 

patchy

adj
  • Not constant or continuous; intermittent or uneven. 

  • Full of, or covered with, patches; abounding in patches. 

How often have the words erratic and patchy occurred in a corpus of books? (source: Google Ngram Viewer )