Choi:All other factors being equal, children whose parents earned doctorates are more likely to earn a doctorate than children whose parents did not earn doctorates.
Hart:But consider this: Over 70 percent of all foctorate holders do not have a parent that also holds a doctorate.
为什么Hart's consideration doesn't contradict Choi's claim?
我是这样想的：
一共20个parents：10个doc parents ＋10个nondoc parents
生的kids earn doc的：6个doc kids ＋4个doc kids
这时Hart说all doctorate holders能不能看成是那些earn doc的kid呢？这些kids毕竟也可以说是doc holders啊。如果这样可以的话，就推出在所有kids earn doc里面，即这10个doc kids里面，有7个是non doc parents生的。矛盾了……
哦，懂了。我的假设第一步就进误区了。实际上doc比nondoc家长要少，所以不能用10doc＋10nondoc来表示。
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