(Excerpt from The Psychology of Money by Morgan Housel)
Graham was constantly experimenting and retesting his assumptions and seeking out what works—not what worked yesterday but what works today. In each revised edition of The Intelligent Investor, Graham discarded the formulas he presented in the previous edition and replaced them with new ones, declaring, in a sense, that “those do not work anymore, or they do not work as well as they used to; these are the formulas that seem to work better now.”
One of the common criticisms made of Graham is that all the formulas in the 1972 edition are antiquated. The only proper response to this criticism is to say: “Of course they are! They are the ones he used to replace the formulas in the 1965 edition, which replaced the formulas in the 1954 edition, which, in turn, replaced the ones from the 1949 edition, which were used to augment the original formulas that he presented in Security Analysis in 1934.”
…Just before he died Graham was asked whether detailed analysis of individual stocks—a tactic he became famous for—remained a strategy he favored. He answered:
In general, no. I am no longer an advocate of elaborate techniques of security analysis in order to find superior value opportunities. This was a rewarding activity, say, 40 years ago, when our textbook was first published. But the situation has changed a great deal since then.
What changed was: Competition grew as opportunities became well known; technology made information more accessible; and industries changed as the economy shifted from industrial to technology sectors, which have different business cycles and capital uses.
Things changed.