LP#
1549505: add flag to tweak popularity-adjusted relevance
This adds a new global_flag, search.max_popularity_importance_multiplier,
to control the factor by which popularity affects Popularity Adjusted
Relevance ranking.
The value should be a decimal number, typically between 1.0 and 2.0:
* 1.0 be would be equivalent to not adjusting relevance for popularity
at all.
* 1.1 would mean that the multiplier would range from 1 (for zero
popularity) to 1.1 (for maximum popularity), for a maximum boost of
10% of the base relevance value of the record.
What's happening in the code:
Scale the 0-5 effect of popularity badges by providing a multiplier
for the badge average based on the overall maximum multiplier. Two
examples, comparing the effect to the default $max_mult value of 2.0,
which causes a $adjusted_scale value of 0.2:
* Given the default $max_mult of 2.0, the value of
$adjusted_scale will be 0.2 [($max_mult - 1.0) / 5.0].
For a record whose average badge score is the maximum
of 5.0, that would make the relevance multiplier be
2.0:
1.0 + (5.0 [average score] * 0.2 [ $adjusted_scale ],
This would have the effect of doubling the effective
relevance of highly popular items.
* Given a $max_mult of 1.1, the value of $adjusted_scale
will be 0.02, meaning that the average badge value will be
multiplied by 0.02 rather than 0.2, then added to 1.0 and
used as a multiplier against the base relevance. Thus a
change of at most 10% to the base relevance for a record
with a 5.0 average badge score. This will allow records
that are naturally very relevant to avoid being pushed
below badge-heavy records.
* Given a $max_mult of 3.0, the value of $adjusted_scale
will be 0.4, meaning that the average badge value will be
multiplied by 0.4 rather than 0.2, then added to 1.0 and
used as a multiplier against the base relevance. Thus a
change of as much as 200% to (or three times the size of)
the base relevance for a record with a 5.0 average badge
score. This in turn will cause badges to outweigh
relevance to a very large degree.
The maximum badge multiplier can be set to a value less than
1.0; this would have the effect of making less popular items
show up higher in the results. While this is not a likely
option for production use, it could be useful for identifying
interesting long-tail hits, particularly in a database
where enough badges are configured so that very few records
have an average badge score of zero.
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>