##### Using Multiple Rules to Correct Different Instances of the Same Error

Increasing the specificity of a substitution rule will always lower the false positive rate and increase the false negative rate. For a single rule, if you're uncertain about including more context, it is better to be more specific than too general. Increasing specificity is the only way to lower the false positive rate.

You can lower the false negative rate by creating multiple rules to correct different occurences of the same transcription error. Ensure each rule contains distinctive context that addresses a specific sub-set of errors.

Recall the overly general example "this : fish". Most corrections made by this substitution rule will be false positives. The rule must be made more specific to bring down the false positive rate. In this case, multiple substitution rules should be created with more context. The following example illustrates multiple substitution rules with minimal contextual information to correct different instances of the same transcription error.

fresh this : fresh fish
quality this : quality fish
this market : fish market
this store : fish store

### Note

The last two rules are risky. Imagine someone saying “I visited this store” or “I’m bullish in this market.” More context to increase specificity will help, if available. However, if fish is frequently mentioned, the last two rules might be acceptable. Substitution candidates should be carefully validated to ensure the false positive rate of each rule is acceptable.