the largest VIF is greater than 10 (or the tolerance is below 0.1) then this indicates a serious problem (Bowerman & O’Connell, 1990; Myers, 1990). If the average VIF is substantially greater than 1 then the regression may be biased (Bowerman & O’Connell, 1990). Tolerance below 0.2 indicates a potential problem (Menard, 1995).
