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# Use the BIAS Field Specifier to Boost Relevance

The `BIAS` field specifier allows you to bias the score of results at query time according to the numerical proximity of the specified field to a particular value. It ignores initial dollar ($), pound sign (£), or hyphen (–) characters in the field names.

Specify `BIAS` in the format:

    BIAS{optimum,range,percentage}

where:

`optimum` | is the value that the field must contain to increase or decrease the result weight by the maximum `percentage`.
`range` | is a positive number that determines the range of the `optimum`. If the specified field contains a value that is in the range of (`optimum` – `range`) to (`optimum` + `range`), the result weight increases or decreases according to the specified `percentage`.
`percentage` | is a percentage in the range`–100` to `100`. If the value of the specified field is in the specified range, the score of the result increases or decreases according to how close the value is to the specified `optimum`.

For example:

-     http://IDOLhost:port/action=Query&FieldText=BIAS{100,50,10}:*/PRICE

  A document whose `PRICE` field value is within the range 50 either side of 100 has its weight increased on a linear scale from 10 percent if the price is 100, to 0 percent if the price is 50 or 150:

-     http://IDOLhost:port/action=Query&FieldText=BIAS{100,50,-10}:*/PRICE

  A document whose `PRICE` field value is within the range 50 either side of 100 has its weight decreased on a linear scale from –10 percent if the price is 100, to 0 percent if the price is 50 or 150:

- You can also use the `BIAS` field specifier to bias the score of results according to the numerical proximity in their `autn_date` metafield to a particular value. For example:

      FieldText=BIAS{1103918400,259200,25}:autn_date

  A document whose `autn_date` field value is within the range 259200 either side of 1103918400 has its weight increased on a linear scale from 25 percent if the price is 1103918400, to 0 percent, if the date is 1103659200 or 1104177600.

Related Topics

- Metadata Fields

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