<p><pre><code>    geared towards quick cheap labor for the PI&#x27;s idea. 
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I am not sure the phrase &quot;quick cheap labour&quot; really gets to the heart of the matter.<p>The real reason why most PhD students work on their supervisor&#x27;s ideas is different. Most students would drown in the ocean of possible ideas, would simply fail without strong guidance from an experienced supervisor. It&#x27;s probably best to see a PhD as a warm-up exercise for future research. The ocean of previous research one must master before being able to do original research in mature fields is simply so large that most students can&#x27;t handle it on their own. Supervisors would love PhD-students who are intellectually mature enough to come up with their own ideas and execute them to a publishable standard. In my experience, at best 1 in 5 PhD students can do this.<p>I used to think my own PhD work was 100% self-invented. But now, having supervised a lot of my own students, I see clearly how my intellectual mentor gently nudged me in the right direction at all critical junctions where I would have gone astray otherwise. Without him, I too would have failed.<p>US PhD typically last a lot longer than UK PhDs, so comparing the two is difficult. I&#x27;d say UK PhD+postdoc is a probably comparable with an US PhD.