Assignment Problem: You are conducting research comparing the effects of various treatments on the management of pain in Rheumatoid Arthritis. Pain is measured on a continuous pain scale. Your study design includes equal members of 3 groups which are defined as treatment (methotrexate treatment, Enbrel (TNF inhibitor) treatment and placebo treatment). Other independent variables are gender, age (dichotomous <35 years or > 35 years), severity of arthritis (categorical: mild, moderate or severe). What type of statistical method of multivariable analysis would you use in this example and why?