Answer: Variables that need to be included or excluded are defined by the research being done and its limitations also.
OR Inclusion and exclusion criteria may include factors such as age, sex, race, ethnicity, type and stage of disease, the subject's previous treatment history, and the presence or absence (as in the case of the “healthy” or “control” subject) of other medical, psychosocial, or emotional conditions.
I believe the tone is kind of sad. The mood the author wanted to make was sadness. He wanted you to image him when he was younger. (i hope this helped)
