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The first lecture on mental levels explains the difference between intelligence and knowledge, likening intelligence to printing presses of various stages of complexity and knowledge to the raw material fed to them. It speaks of the first method of determining intelligence of persons introduced by Binet about 1905 and explains the accuracy of various tests as determining mental level, quoting Army Alpha tests.
The second lecture is on efficiency, which consists in fitting people into work at the level of their intelligence, on their emotional control, temperament, and physical conditions. Ability to adapt one's self to one's environment is an index of mental level.
The next lecture is on the delinquent, or the person who neglects his duty. He impairs the efficiency of the group. He may be delinquent "because he does not know any better or because he cannot help it." There is the high percentage of low mental
Human Efficiency and Levels of Intelligence.. Arch NeurPsych. 1928;20(1):233. doi:10.1001/archneurpsyc.1928.02210130240023