The number parameter
is a number in the range 0..255 that defines
how a document popularity affects
is score in search results.
The default value is 16.
If PopularityFactor is set to a non-zero value, then the document with higher popularity are ranked higher.
In order for PopularityFactor to have effect at search time, popularity should previously be calculated during an indexer --index or index --rewritepop run.