The phrase "importance in determining" is grammatically correct and can be used in written English.
Example: Understanding the potential risks and benefits is of great importance in determining whether to undergo a medical procedure.
Energy security and public safety should be of equal importance in determining future policy on nuclear power.
The amount of available oxygen is of critical importance in determining which volatile gases are present.
The answer to this is of key importance in determining whether war against Iraq makes any sense from the F.B.I.'s internal security point of view.
But it does not follow from this that education will be of similar importance in determining the total amount of mobility within society at large.
But Judge Pauley said receiving academic credit was of little importance in determining whether interns should be paid.
The temperature occurring at this interface is of critical importance in determining how suitable a location is for different forms of life.
In modern moral and legal thought, actual consent whether express or tacit is of great importance in determining the force of moral obligations and the validity of contracts.
Because these chemicals affect the behaviour and fitness of animals that encounter them, they are of major importance in determining the range of plants eaten by an animal.
Detection of vibrations on the lunar surface by seismographs is of fundamental importance in determining the internal structure, physical state, and tectonic (crustal) activity of the Moon.
This free-float adjustment will reduce the market capitalization (stock price times shares available for purchase) of many stocks, lowering their weighting and importance in determining how much the indexes go up or down.
However, each one of those lithological units has no equal importance in determining and controlling groundwater.
