In fact, there are two types of density, according to a recent study by PeterGordon of the University of Southern California and Sanford Ikeda of the State University of New York, Purchase.
Like Peter Robinson and Gordon Brown he had been a number two for some time and, like them, it was always believed he would eventually get the top job.
It is also claimed that Mr Prescott's role as deputy prime minister has been diminished over the months and that Chancellor Gordon Brown and Northern Ireland Secretary Peter Mandelson are effectively acting as joint deputies.