Market Breadth Primer: Advance / Decline Issues
Advance Issues is the number of stocks traded above their previous trading day close within a particular basket. For example, New York Stock Exchange provides the advance issues data across all the stocks traded on its board throughout the day. That is called the NYSE Advance Issues.
Decline Issues is the number of stocks traded below their previous trading day close within the same basket as the advance issues, as they are often quoted together as a pair.
Here is an example on how this pair of data look like.
Advance/Decline Issues are the most common market breadth data that is mentioned frequently in television and financial websites. They are also the most common components for the construction of breadth indicators. In general, on trading days when the indices are positive, you will find that advance issues is greater than decline issues, and vice versa.