Why does a PhD in the US take so long?

I'm taking my preliminary exams in less than a week's time so I thought it might be a good time to highlight some of the differences between PhD programs in the US and in universities outside the US. When I tell my friends that I will take at least 5 years to finish my PhD in political science in the US, more often than not, the question back to me would be, "Why so long"? The people with PhDs in Malaysia, I'm guessing, come disproportionately from universities in the UK, Australia, Malaysia and New Zealand and they usually take approximately 3 years to complete. Why this disparity?

The main difference lies in the coursework requirements. Almost any PhD program worth its salt in the US requires its students to complete at least 2 years of coursework before they are even allowed to start on their PhD proper. I'm almost at the end of my two years at Duke and I'm one of the few students from my cohort taking my prelim exams this early. Most of my cohort are taking the prelims in 6 to 9 months' time which means they would have finished at least 2 1/2 years of coursework.

Why have this coursework requirement? At least for the social sciences, it is to ensure that you are familiar with a broad enough 'vision' of your field of study before embarking on your 'narrow' PhD thesis focus. I feel that this is one of the great strengths of the US PhD. You are exposed to different fields besides your main area of interest. You are thus able to borrow different techniques and ideas from different fields.

The coursework requirements often have some 'technical' elements. For political scientists who want a teaching job in the US system, statistical and mathematical knowledge is almost a 'must have' (unless you are a political theorist). You'd be surprise that a lot of what passes for political science here in the US comprises of regression anaylsis, game theory and models filled with equations. Those who want to skip these technical elements have the choice of learning 2 or more foreign languages. In practice, what you find is that most political scientists would be proficient in at least one foreign language and at least some quantitative methods.

I recognized the strength of the US PhD program even before coming here. Now that I am here, I value it even more. It provides necessary training and it inevitably increases the quality of your work at the thesis stage.

I'm not saying that coursework is not a requirement in other non-US universities. Increasingly, it is becoming the norm in many economics programs in the UK (at least at the LSE and Cambridge) where taking and passing one year of coursework is mandatory. I'm not sure about the current situation in Australia and New Zealand.

As more and more academics are trained through the US system, I believe that a US PhD will be valued more highly than a PhD from the UK, Australia or New Zealand, at least among the members of academia. I know that I will be getting a lot of flak about this but it's a general position that I'm willing to stand by and defend.