I have a question regarding a likert scale. I am doing a survey containing 6 responses for the likert scale's questions : the five gradual usual response, and "I am not sure (yet)". I want too exclude the last one (the 6th) from the mean calculation (to attribute no value). I read I can do this with "Missings", but I did not find a precise way. I am new at coding , could someone explain me how to insert this missings please?