The phrase "ascertain how important" is correct and usable in written English.
You can use it when you want to determine the significance or value of something.
Example: "We need to ascertain how important this project is to our overall strategy before allocating resources."
Alternatives: "determine the significance" or "evaluate the importance".
It would be important to ascertain how healthcare workers' opinion about the vaccine affects health, especially reproductive health.
However, it is important to ascertain how activation to the higher-level baseline condition itself might change over age.
In future work it will be important to ascertain how the synthesis of GDF5 is controlled as this has a bearing on understanding how GDF5 participates in the regulation of dendrite growth and elaboration.
Since the phenotypic differences between Maythorpe and Golden Promise were pleiotropic, it was important to ascertain how early in seedling development the difference between the two cultivars at expression level becomes apparent.
Our objectives were to determine what proportion of patients think prognostic information is important, the reasons they give for (not) why they feel prognostic information is important, and to ascertain how often patients feel that their prognosis is discussed in the consultation.
With this year's candidates professing primarily Judeo-Christian traditions, we at the Opportunity Agenda believe it's important to lift up the foundational social justice values, ideals, and policy principles of those traditions to ascertain how consistent the candidates' stated positions are with the faiths they espouse.
How might I be perceived?" And use supervision to ascertain how others perceive you.
Nor can we immediately ascertain how deep such influences have gone.
It was still possible, she announced, to ascertain how the 21 victims had met their deaths.
