"had the highest proportion" is correct and can be used in written English.
For example, "The students in the green group had the highest proportion of passing grades on their final exam."
Uganda had the highest proportion of entrepreneurs of all, 29.2%.
Latvia, at No. 58, had the highest proportion, with 51.8percentt women scientists.
Ealing in London had the highest proportion of Polish-born residents.
In 1931, France had the highest proportion of immigrants of any western country.
Middlesbrough had the highest proportion of obese children just starting out in school – 14.7%.
Ejaculates in the high motility category also had the highest proportion of morphologically intact spermatozoa.
Two of the networks with the lowest need had the highest proportion of beds.
Barcelona, the runners-up, had the highest proportion of their squad playing regular international matches.
A generation ago, the United States had the highest proportion of college graduates in the world.
At the university level, Victoria had the highest proportion of international enrollment of any Australian state.
Using multivariate regression, we found that foreign applicants to the USPTO had the highest proportion of citations added by examiners.
