Quote: Very interesting. In 1963 didn't almost all pro games in Japan use 4.5 komi? It is surprising that amateurs would make a 2 pt. leap at that time.
No. For amateurs it was only a 1-point leap anyway.
The Oza began using 5.5 in 1955, just before the NHK Cup, and other events such as the Meijin and Judan followed suit in the very early 1960s. But the Honinbo and Nihon Ki-in Championship held out until 1975.
According to various articles discussing komi before and after the war (of which there were many), it seems that pro opinion had favoured a komi of 5 points for quite a long time. At the time, with few knockouts, there was no need to worry much about jigos. But amateurs had to worry about jigos in knockouts and they had been playing with 5.5 komi for a long time. When the time came, in 1949, for the pro world to write down its rules for the first time, they also had to make a decision on how to handle jigos. Since there were still many players who believed komi go was not go (it was not that they believed Black had no advantage - rather they believed, in those more leisurely days, that a contest should be settled on the basis of a series of games at traditional handicaps, e.g. B-W-B), a nod in their direction was made by unrounding 5 down to 4.5 instead of up to 5.5 as was then usual in the amateur world.
The amateur view was largely influenced by mathematical arguments. Indeed, Japanese amateurs were also adventurous early on with things like free handicaps, which are not as new as often claimed, and alternative rating systems. But pros were not specially antediluvian. Even among pros, there is also a long history of unusual komis being used in events such as the insei leagues (e.g. White giving komi, komi 2.5 points, etc). But in the frontline events, tradition had its place.
When the Oza began, the sponsors respected that by actually balloting pros. They voted by a large majority (22-2 if memory serves) for the large komi (5.5) around 1955 but diplomatically accepted retention the smaller komi in existing events. There was some confusion anyway, in that in quicker games at 4.5 komi Black was apparently winning almost nine out of ten games, but in the slow Honinbo only one out of three. They felt this must mean something, but no-one seemed to know quite what!
Japan's shift to 6.5 stemmed mainly from concern, even then in the late 1990s, over the risk of falling behind internationally. There doesn't seem to be much interest in a higher komi yet. The latest figures from Japan I've seen, in 2008, showed that a komi of 6.5 still leaves Black an edge, but a very slight one. In 19,702 games from 6 November 2002 up to 31 December 2007, Black won 50.59% and White won 49.41%.
A slightly crude comparison, of all games in the GoGoD database from 2008 on (8192 games), gives a Black win ratio of 50.4% and White 49.4% (0.2% void, jigo or unfinished).
Rather than achieve parity, 7.5 might just flip those figures, but there is no incentive to try it to find out.
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