# Balance Precision and Recall

In many cases, Eduction is able to locate entities that are ambiguous, such as a postal code which is simply a five-digit number. In some situations it is desirable to match as many entities as possible ("high recall") and in others only entities with a high likelihood of being a useful match ("high precision"). Each match is given a score value so that you can filter the results.

As described in Entity Context, matches located by an entity that requires context are assigned higher scores than matches located by the corresponding entity without context. Most matches extracted without context have a score of `0.4`. For example, a context-free date ("January 18, 1998") might be returned by a Date Of Birth entity with a score of `0.4`. But with context to suggest that it is indeed a date of birth ("DOB: January 18, 1998"), the score should be above `0.5`.

The PII post-processing script (see Configure Post Processing) includes a step to validate matches (for example, it can validate some ID numbers by calculating a checksum). The script increases the score of matches that have valid checksums, because this is an indication that the match is more likely to be genuine. Any match that has an invalid checksum is immediately discarded because it cannot be genuine.

When you configure Eduction, use the parameters `MinScore` and `PostProcessThreshold` to achieve the desired balance between precision and recall. Eduction discards any match with a score lower than `MinScore`. Matches with scores that meet or exceed `MinScore` are then processed by post-processing tasks. After post-processing has finished, Eduction discards any match with a score lower than `PostProcessThreshold`.

In the example configuration that is included with the IDOL PII Package, `MinScore` is set to `0.4` and `PostProcessThreshold` is set to `0.5`. These values have been chosen to return results only if they have a relatively high likelihood of being a useful match. Any match that is located without context can proceed to post-processing, but, unless its score is increased through successful validation, it is then discarded. If you prefer to maximize recall rather than precision, you can reduce or remove these thresholds.

For more information about Eduction configuration parameters, refer to the Eduction User and Programming Guide.

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