The main metric for the background linking task in 2018 was nDCG(5), using exponential gain values. The values map to the following judgments:

• 0: The document provides little or no useful background information.
  
• 2: The document provides some useful background or contextual information that would help the user understand the broader story context of the target article.
  
• 4: The document provides significantly useful background ...
  
• 8: The document provides essential useful background ...
  
• 16: The document _must_ appear in the sidebar otherwise critical context is missing.