Earliest citation for truth density I am searching for a citation of a formula that calculates the proportion of true (1) outcomes in the corresponding truth table of a boolean function. Searching a little bit in the Cryptography literature, I found that the hamming weight of a boolean function is defined as the number of $1$'s, so it is close to the metric I am referring to. I have also seen this metric/property mentioned as 'truth density' in Wolfram, see an example.
Has anybody used this formula in a paper before ~2000-2010s? (a recent paper that defines it as bias is this one). Or maybe provide a proper (older) publication to cite for the hamming weight?
The truth density $p$ is arguably the same concept as the bulge to 0 $b$ of a Boolean function as $b=1-2p\iff p=(1-b)/2$. The bulge leads to cleaner formulae in many cases though. The language of bulges was common at Bletchley Park. Do you count the General Report on TUNNY as a 1945 or a 2015 publication?