为什么 are more likely to have been,可以这样用?have been 可以去掉吗?

为什么 are more likely to have been,可以这样用?have been 可以去掉吗?
If you were to examine the birth certificates of every soccer player in 2006's World Cup tournament,you would most likely find a noteworthy quirk;elite soccer players are more likely to have been born in the earlier months of the year than in the later months.