According to a 1996 study published in the Journal of Human Resources, Americans (of Middle Eastern descent) were twice as likely as the average American (were) (to be self-employed )
(were)可以省略在于可以明显看出是S.和S.比 Americans 和 the average American
通常保留动词或助动词在于如果动词或助动词省略会误认为是S.和 O.比
Ex.Prep1-128
According to a study published in The New England Journal of Medicine, aspirin prevents blood clots just as well as a commonly used and more expensive blood-thinning drug does.