In the United States, colleges and universities require that the student hold an undergraduate degree and, in some cases, a master's degree prior to beginning a doctoral program.
There are two types of doctoral degrees: research and professional.
A research doctorate is awarded upon a completion of a thesis in a field of research and the most common type is the doctor of philosophy (Ph.D.). Students can earn a Ph.D. in a variety of humanities and scientific fields, ranging from classics and English to astrophysics and chemistry. Other types of research doctorates include the doctor of engineering (D.Eng.), awarded to students upon completion of significant research in a field of engineering, and doctor of education (Ed.D.), earned by students in the field of education.
A professional doctorate or first professional degree is awarded to doctoral students in fields that do no engage in scholarly research but instead in a profession. These include such professions as medicine (doctor of medicine or M.D.), law (juris doctor or J.D.), veterinary medicine (doctor of veterinary medicine or D.V.M.) and dentistry (doctor of dental surgery or D.D.S.).
Traditionally earned in classroom settings, many doctoral degrees (mainly research doctorates) can also now be earned online. While some law-school programs of study can be pursued in an online setting, most professional doctorates are not yet available in this format due to the fact that they require extensive hands-on experience.
Doctoral degrees can be completed in anywhere from three to eight years of full-time study. While law school is typically completed in three years and medical school in four years, according to the National Science Foundation, the median time to earn a research doctorate in the U.S. is 7.5 years.
The U.S. Census Bureau has determined that education level has a direct relationship to the size of the paycheck. A person with a bachelor's degree makes an average of $45,500 per year and $54,500 with a master's degree. On the other hand, the average salary of an individual with a research doctorate is $81,400 and $99,300 with a professional doctorate.