这种做法缺乏理论依据：所有股市的预期回报率理论上是一样的。
This is without theoretical justification, which points to expected returns in all stock markets being the same.
科学家们趋向认为它的背后的科学是相互冲突的，或者宁愿是缺乏理论依据的。
Scientists tend to be conflicted about the science behind it, or rather the lack thereof.
神经网络具有自学习，自适应，并行处理的能力，但结构的选择缺乏理论依据。
Neural network have the abilities of self-learning, adapt and parallel management, but the structural selection lacks academic bases.
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