##### Best Practices for Creating Substitution Rules

Substitution rules work best when they are not too general and not too specific. Rules that are too general will cause substitutions to match and replace when they should not. This case is known as a false positive. Rules that are too specific won't allow substitutions to match and replace where they're supposed to. This case is known as a false negative. Develop your substitution rules to strike a balance between the potential risk of false positives and false negatives. A good substitution rule has just the right amount of specificity.

The following is an example of a substitution rule that is too general and would result in false positives.

this : fish

The substitution rule above seems like an obvious solution if the word "fish" was consistently mistranscribed as "this". However, the word "this" is used frequently. Therefore, every time the word "this" is spoken, it would convert to "fish". The overly general substitution rule above would cause more transcription errors than it would correct. The solution is to add some context to make the matching phrase more specific.

fresh this : fresh fish
quality this : quality fish
bad this : bad fish

The following is an example of a substitution rule that would result in false negatives.

My name is fred and I'm on les sick : My name is fred and I'm on /Lasix/

The substitution rule above contains too much context and will fail to correct most occurrences of "les sick". Avoid making overly specific substitution rules like the one above as they miss the majority of opportunities to correct an error. The following example illustrates a more effective substitution rule with less context.

les sick : /Lasix/

If the mistranscription was "less sick" instead of "les sick", a substitution rule similar to the one above would be too general. It wouldn't be out of the ordinary for someone to say "I feel less sick today". In this instance, adding some context to the rule would make the necessary corrections.

on less sick : on /Lasix/

It might be tempting to add more context to the rule above. Such as, "I'm on less sick : I'm on /Lasix/". However, that would result in false negatives as it would fail to correct phrases such as, "I'm not on less sick" or "My dad is on less sick".

Being overly specific will limit the effectiveness of your substitution rules. The following is another example of a substitution rule with too much context.

Welcome to Wells Fargo for a change : Welcome to Wells Fargo /Foreign/ /Exchange/

The substitution rule above is ineffective because it would fail to correct other instances of the same transcription error. Consider the following mistranscribed phrases.

• "Good morning, this is Jim from Wells Fargo for a change"

• "Thank you for calling Wells Fargo for a change"

The following substitution rule will correct the same transcription error in different contexts like the ones listed above.

Wells Fargo for a change : Wells Fargo /Foreign/ /Exchange/