unpredictability vs variability

unpredictability

noun
  • The quality of being unpredictable. 

  • Something which is unpredictable. 

variability

noun
  • The state or characteristic of being variable. 

  • The degree to which a thing is variable. In data or statistics this is often a measurement of distance from the mean or a description of data range. 

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