As with all social classes in the United States, there are no definite answers as to what is and what is not middle class. Sociologists such as Dennis Gilbert, James Henslin, William Thompson, and Joseph Hickey have brought forth class models in which the middle class is divided into two sections that combined constitute 47% to 49% of the population. The upper middle or professional class constitutes the upper end of the middle class which consists of highly educated, well-paid professionals with considerable work autonomy. The lower end of the middle class – called either lower middle class or just middle class – consists of semi-professionals, craftsmen, office staff, and sales employees who often have college degrees and are very loosely supervised.