I took the average number of medals won by each host in the years before their Olympics and compared this to the number won when they were the host. Thanks to the cold war boycotting of the 1980 and 1984 games, the USA and South Korea were excluded because they missed a preceding Olympics and the USSR is excluded because its success at the 1980 Moscow games was at least partly due to the absence of the other superpower. West Germany was excluded because it did not compete under that name until 1968.
Here are the results. Click to enlarge. Each nation's home performance is shown in the middle. Figures to the left show preceding Olympic performances going back up to seven Olympics.
As you can see, every host nation wins significantly more medals when they are playing at home. Plausible explanations include increased investment in athletics prior to the the games, favourable climatic conditions, psychological advantages from crowd support and judges being influenced by partisan crowds.
The win rate increases from 41% (Australia, 2000) to 756% (Spain, 1992). This, of course, is a large margin, but the average increase in medal tallies is 222%. Therefore, if 'Team GB' benefits from an average home advantage, we would expect them to win 64 medals this year.
