A typical career progression would see a porter advance to become a head porter, then a ticket collector or booking clerk, which could in turn lead to the senior roles of assistant station master or station master. Other career progressions were also common on some railways. Research at the London School of Economics has shown (with particular reference to the Great Eastern Railway) how advances in rail signalling in the late Victorian era led to a shortage of skilled labour, with many unskilled porters advancing to porter signalman, and ultimately qualifying as signalmen.