I'm confused by the number of factors in an experiment. This example makes it seem as though there is only one factor "Treatment". So if an experiment looked at the effects of a treatment and one received treatment and one group received the placebo. Would there be one or two factors? Does the placebo group count as it's own factor outside of "treatment"?

llig flealuff factors, all infants enrolled in the study were otherwise healthy. This experiment compares 2 treatments: immediate probing and deferred treat ment. There is a single factor: "treatment type." The subjects are infants diagnosed with blocked tear duct and the main response variable is the time of symptom resolu tion. (The researchers also recorded all related medical care and associated costs.)