"demonstrate higher levels of" is correct and usable in written English.
It can be used when referring to a group's performance or when comparing one group's performance to another's. For example: "The students in this class demonstrate higher levels of academic excellence compared to those in the other class."
Significantly, subjects who watched the comedy film but did not report higher levels of happiness were unable to demonstrate higher levels of productivity.
Studies from San Diego State University compared homosexual civil unions and heterosexual marriages in Vermont and found that the same-sex relationships demonstrate higher levels of satisfaction, sexual fulfillment and happiness.
University-based PRCs have higher levels of short-term additionality, demonstrate higher levels of organisational innovation but prove less sustainable.
We find that larger firms, firms with greater free cash flow, and higher advertising outlays demonstrate higher levels of corporate social responsibility (CSR).
Recent reports that habitual marathon runners demonstrate higher levels of stiffness and cardiovascular risk factors have been of great interest to the medical and scientific community.
The solar flares of similar class demonstrate higher levels of ΔA values during periods of low solar activity than during the period of moderate solar activity for both signals.
Canada's immigration minister Jason Kenney said earlier this year that some immigration applicants will soon have to demonstrate high levels of English or French fluency to gain entry to Canada.
Newly graduated nurses need to demonstrate high levels of competencies when they enter the workplace.
Additionally, group posts as illustrated below demonstrate high levels of respect for sheiks and their discursive schemas.
We were able to demonstrate high levels of luciferase activity with this construct; however, selectivity was lost.
Chinese communities in North America demonstrate high levels of both educational attainment, and household affluence.
