The phrase "ascertaining how often" is correct and usable in written English.
You can use it when discussing the frequency of an event or action, often in research or analytical contexts.
Example: "The study focuses on ascertaining how often participants engage in physical activity each week."
Alternatives: "determining the frequency" or "finding out how often".
The charity's head of policy for Scotland, Richard Meade, said: "We call for an urgent investigation of the situation across Scotland to ascertain how often people with a terminal illness are being denied the support they are entitled to at a time when they need it most.
We calculated the number of p-values that were less than 0.05, in order to ascertain how often each test rejected.
The method(s) used to identify relapse was identified to ascertain how often a rise in LDH helped to detect relapse.
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.
This pattern was quite intriguing (a nearly ubiquitous assumption with genome-wide expression arrays is that expression-level data are normally or log-normally distributed), and led us to ascertain how often such patterns occurred, and whether such were associated with diabetes-related phenotypes.
Mr. Peters said he could not immediately ascertain how frequently such incidents occurred.
Ascertaining how, when and how often consumers use healthcare services is critical to effective healthcare policy and funding.
To survey active vitreoretinal surgeons to determine how often they intentionally debride the corneal epithelium during vitrectomy surgery for diabetic patients and to ascertain whether the selection of the surgical lens type influences the debridement rate.
Ascertaining how participants were coping with their health.
