One of the first statistics that someone who is researching religion in Japan will come across is that when statistics are collected the total membership of the main religions when added together equates to almost double the population of Japan. So for instance, in 2006 the Japanese Agency for Cultural Affairs reported that there were 106.8 million Shinto adherents and 91.2 million Buddhists while the total population of Japan was 127.8 million people.
The explanation for these strange statistics is very straightforward- in Japan most people do not regard religions as exclusive and this includes the various temple and shrine authorities who collect the statistics. This attitude is illustrated quite nicely by the fact that it is common in Japan for a person to have Shinto ceremonies shortly after they are born and at certain ages (3, 5 and 7) throughout their childhood, have a Christian wedding when they get married and have a Buddhist funeral after they die. It is also relatively common for individuals to be unaware of what Buddhist sect they and their family belong to until after a close relative dies and they need to contact a temple and summon the relevant priests.