I think this particular advice from The Intelligent Investor is unreliable. Back then, bond yields were substantially higher, dividend yields were significantly higher, equity valuations we significantly lower, etc etc. The rest of the book is top notch though.

The Intelligent Investor was not written in a time when interest rates were zero (and real interest rates were negative).

Using the suggested approach would demolish a bond portfolio. Assuming Barclays Aggregate index as a proxy, if interest rates rise to 7%, then half the value of the bonds would be lost.

Note that correlation of rising rates and rising stock market exists until about the 4-6% rate region before the market starts to be truly negatively correlated with bonds above that number.

Based on all my reading over the past several years, this is the first time in history that so many bonds have been priced at or near zero (including below zero rates). I think Benjamin Graham would be writing a supplement to his book if he were alive today.