I work on a CRM system for healthcare and there's a feature where we send an SMS to a patient reminding her of some scheduled consultation. The patient can then answer the SMS with either "yes" or "no" to confirm she's gonna show up or to cancel the consultation - the system tries to recognise a positive/negative answer by doing some very ingenuous and cheap checks and then updates the status of that consultation.
The problem we have is that users don't always answer "yes" or "no" - despite the fact that that's explicit explained in the body of the SMS; they very commonly answer something like "oh, very nice, thanks, I'll show up" or "gosh, I'm stuck in a traffic jam, won't do it", or even "nice, can you confirm the address please?".
That happens a lot, and we can't identify those as positive or negative - not without investing in some heavy natural language processing, which is not our point. The challenge here seems to be making clear for the user that he should answer with only "yes" or "no", but we're failing on that.
The current SMS text follows:
#{patient_name}, your consultation is scheduled to #{consultation_date} at #{consultation_time}. Answer for free YES to confirm your presence or NO to cancel it. #{doctor_name}
Is there some way we can assure we clearly instruct the patient how to answer while dealing with a 150 characters limitation?
Edit:
Currently, when we can't recognise an answer, we send it as an email to the clinic explaining the situation. That's OK, the clinic can then deal with it manually, but that's kind of killing the automatic confirmation/cancelation of scheduled consultations.