In the beginning of an experiment, subjects are required to report on their initial emotions / mood using Questionnaire#1. After the experiment is conducted, the subjects fill another mood questionnaire#2. 

How do we interpret these two sets of data (from the initial questionnaire and the final questionnaire)? 

Since it is not possible for every participant to have the same initial emotions or level on the Likert scale (which goes from *strongly disagree* to *strongly agree*) at the start of the experiment, how do we analyze the data to "normalize their emotions" from questionnaires.