Sociologists Dennis Gilbert, William Thompson, and Joseph Hickey, however, only divide the middle class into two groups. In their class modes the middle class only consists of an upper and lower middle class. The upper middle class, as described above, constitutes roughly 15% of the population with highly educated white collar professionals who commonly have salaries in the high-5-figure range and household incomes in the low-6-figure range. Semi-professionals with some college degrees constitute the lower middle class. Their class models show the lower middle class positioned slightly above the middle of the socio-economic strata. Those in blue- and pink-collar as well as occupations are referred to as working class in these class models.