At that time, psychologist J.C. Flugel and others did some sporadic research on this, but there were some loopholes in theory and method. 193 1 year, Chen Li combined psychophysics and psychometrics to overcome the difficulty of lack of experimental instruments and equipment, and selected 120 junior high school students as subjects to study the fluctuation of intellectual operation and sensory threshold. This is a complex laboratory study, which uses the most extensive materials and individual subjects, verifies the determination of O factor in detail, and confirms the change cycle of O factor.

From the content, this study pushed Froegel's research on O factor from fatigue to attention. This makes the research not limited to a single factor. In methodology, we should break through the limitations of a single factor in various ways. In this study, Chen Li also put forward different views on single factor analysis, namely, Spearman's four-difference method, which tends to be multi-factor and breaks through Spearman's research framework. As a result, I wrote my doctoral thesis "Sensory Threshold and the Ups and Downs in Intellectual Activities". Spearman quoted it in his two-volume book Psychology of Past Dynasties. Frog summarized the paper into "The Latest Discussion on Intelligence Fluctuation" and published it. The last chapter of the paper, O Factor Fluctuation Cycle, was published in British Psychology. Because of its moving average method, the measurement of time phase is handled in a new way. The improvement of this statistical method has been praised by peers. An Australian psychologist called it "a new model of stage analysis".