There are three ways of attaching the neck to the body of an electric guitar: set necks where the neck is glued to the body with a tenon joint (most Gibson guitars), through necks where the neck & body are made from the same piece of wood and bolt-on necks (most Fender guitars). It is almost a given amongst guitar players, that through necks sustain better than set-necks and bolt-on necks have the worst sustain.
Luthier and scientist R.M. Mottola decided to test this received wisdom, and he published his surprising results in the American Lutherie journal. He made three instruments that differed only in their neck joint construction (through, set or bolt-on). He then carried out power analysis, spectrographic analysis, and listening evaluation on these instruments.The power analysis results suggest that the relationship between sustain and neck joint type was the oppositive of the received wisdom on neck joints. Bolt-on necks had the longest sustain and neck through designs had the shortest sustain. The study also included listening evaluations, where people listened to recordings of single notes and tried to pick out the longest sustaining note. They could not detect any difference in sustain between the different neck designs.
People may have played a set-neck Les Paul and found it to sustain better than a Fender strat and then jumped to the conclusion that set necks sustain better. What they should have done is compared a set neck Les Paul with a bolt-on Les Paul before reaching their conclusion.
Reference Mottola, R.M. “Sustain and Electric Guitar Neck Joint Type” American Lutherie #91, 2007, p. 52.