12. The non-transitory computer-readable medium of claim 11 , wherein the lexical variants are categorized into families of words or word phrases having equivalent meaning or effect.
12. The non-transitory computer-readable medium of claim 11 , wherein the lexical variants are categorized into families of words or word phrases having equivalent meaning or effect. 13. The non-transitory computer-readable medium of claim 12 , further comprising: in response to receiving a positive response rate for a lexical variant of the message text with a particular independent variable word or word phrase, testing other words or word phrases for the independent variable that are within the same family as the word or word phrase of the particular independent variable associated with the positive response rate; and in response to receiving a negative response rate for a lexical variant of the message text with a particular independent variable word or word phrase, testing other words or word phrases for the independent variable that are in a different family as the word or word phrase of the particular independent variable associated with the negative response rate.