at a premium vs thin on the ground

at a premium

prep
  • At a high, or higher than expected, price. 

  • Scarce, in short supply. 

  • Above par value. 

thin on the ground

adj
  • scarce, or difficult to find. 

How often have the words at a premium and thin on the ground occurred in a corpus of books? (source: Google Ngram Viewer )