<p>I think trying to root out PhD students who are still deciding on their life goals is a fruitless exercise, since the vast majority of PhD students are doing that and even the most serious and dedicated PhD student is probably not 100% sure what they want to do with the PhD yet. I was a pretty successful doctoral student - externally funded throughout, including an NSF; several publications; got a postdoc a year before I graduated; and my advisor got tenure in part because of my role in his lab - but I went into the program still deciding on my life goals and realizing that I could walk away with an MA if I didn’t want to finish the program. That’s just reality. You always need to have an exit plan.</p>
<p>Like I said, going to a PhD program with the plan in mind to definitely drop out after you get the MA is completely different than going in with every intention of finishing, but with the knowledge that you can drop out if you decide that the program is not for you. The latter is simply knowledge; it’s like knowing the sky is blue or that bears eliminate waste in the woods. It’s simply a fact.</p>
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<p>As for why PhDs and not MAs, it’s mostly time. New graduate students are much less useful than advanced grad students, unless they have extensive research experience/history. Even then - you have to learn the way the lab works, you have to learn the new data set or experiments, new equipment, perhaps some new analysis methods, new protocols. You have to get on IRB or IACUC protocols. You also need to acquire soft skills, like how to write scientific journal articles (as most have never written one before PhD program), how to assist in grant-writing, and how to present at conferences. There’s a lot of ramp-up time. Also, during most of this time you are taking classes, which diminishes the amount of time you can spend in the lab.</p>
<p>I would say that it probably takes a new grad student at least 1.5-2 years to really get up to speed and to the point where they can work efficiently and semi-independently, without time-consuming guidance from a professor. Dissertation phase PhD students in years 4 and beyond are even better. In fact, I would say that a senior undergrad can probably do most of the same tasks as a first-year graduate student, and they are much cheaper (most of the times free!) If you’re an MA student, by the time you’re more useful and have more available time than a free undergrad, you’re finished and out the door. But as a PhD student, you still have another 3-4 years for the professor to get your assistance. Also, by year three you are largely done with classes, which means you can spend almost all day in the lab if you want (and the professor no longer needs to pay your tuition, which they would if they had to hire another MA student to replace the MA student they just lost).</p>
<p>Not only that, but academia is a slow-moving beast. A grant can take 2-3 years to get funded from conception to grant-writing to acceptance to funding. Projects themselves can be 3-5 years long - it might even be 1-2 years before you have enough usable data to do useful, interesting analyses and get publications. Professors want students who are going to be there long enough to understand the project, get really familiar with the work, and be able to churn out those papers when it happens. If your advisor is just collecting data in your first year of an MA, you might be gone before he starts to write papers. Then he needs another student to help him.</p>
<p>Also, PhDs contribute to the prestige of universities and departments. Universities are more prestigious, and ranked higher, with PhD programs. This happens both directly (the actual existence of the program = higher ranking) and indirectly (PhD students help write grants that bring in more money; they help write papers that increase the visibility of the institution; they hobnob at conferences and give presentations and teach classes and all that). PhD students also graduate and take prestigious tenure-track jobs, which increases the visibility of the program. MA students do that stuff far less frequently - or, in the latter case, not at all.</p>
<p>Postdocs can come on for 2-3 years only because they have the PhD, and so they’ve already got the training. Ideally they’ve already helped co-author some publications, seen the way a grant works, and done some presentations. They can kind of hit the ground running with the postdoc begins. They only need to learn about the project, not learn about how to be an investigator period. Plus postdocs don’t have any distracting obligations to a graduate program. I’m a postdoc now and it’s like heaven to do research all day without worrying about my dissertation or studying for exams or whatnot.</p>