3. The method of claim 2 , wherein: the initial time stamp is different from the time stamp corresponding to starting to provide the prompt; and the final time stamp is different from the time stamp corresponding to stopping to provide the prompt.
2. The method of claim 1 , further comprising: defining, for each prompt, an initial time stamp and a final time stamp, wherein the period between the initial time stamp and the final time stamp constitutes the time period associated with the prompt.