I'm developing an App that saves a user time doing something by giving the user instrcutions every step of the way.
To make it more rewarding to use the App I want to give him some feedback on how much time he saved today/month/week. The overall message should be "You always save time using this App". Especially I want to notify the user about saving time right after he starts the App to not have the reward in some rather distant uncertain future.
When he clicks "start" I can estimate how much time he may save. When he clicks finish (and then I know how much time it actually took), I can tell him something like "You actually saved 10 minutes". But this only applies when everything goes according to plan. For example the user might take a break in between or get distracted by a phone call or don't do everything according to the Apps instructions (thinking he found a shortcut or something).
In any of these cases the statistics are becoming invalid. So doing a straight forward approach the App might conclude "Hey you lost 15mins, because you used the App", when in fact it was 'the useres fault' (which of course I don't want to communicate to the user in that way).
So this is getting complicated rather quickly and I know that my description is rather vague and might leave more questions than answers, but what it comes down to is the following:
What if I took the measurement, gave the prediction to the user right at the beginning and then ONLY if the user actually saved time after he finished, give the user the results and otherwise just drop it. Otherwise I would implement logic that tries to figure out what happened and ask the user what went wrong ("Did you take a break?") etc.. But I find this rather elaborate, because this should be some lightweight feedback and not something that requires too much interaction. Does anybody have experience whether the user might get suspicious, feel betrayed, etc? Keep in mind that (also for the sake of argument) that this is not to cheat the user but rather to avoid the user "cheating" the system. Assume that if the user followed the App, he could NOT lose time.