The phrase "ascertained because" is correct and usable in written English.
It can be used when explaining the reason or cause for determining or discovering something.
Example: "The results were ascertained because the data was thoroughly analyzed and verified."
Alternatives: "determined due to" or "established as a result of".
The full extent of death, injury and destruction cannot be ascertained because of the government's refusal to allow independent media and monitoring in the conflict zone.
De novo missense variants explained a larger proportion of individuals in our series than in other series that were primarily ascertained because of ID.
The association with having ever breastfed could not be ascertained because of an inadequate sample size.
It lasted only three weeks following treatment in a private hospital of which details could not be ascertained because of poor record keeping.
First, false positive error rates can be experimentally ascertained because no CNVs are expected to be found from probes located in the third, fourth, and X chromosomes.
Those whose ACR response status could not be ascertained because of a missing evaluation were considered nonresponders for the relevant time point.
But the true risks are difficult to ascertain because banks do not disclose much about their exposure.
The truth is generally impossible to ascertain because many incidents are not even formally reported, much less investigated.
Worldwide figures are difficult to ascertain because of the wide variety of outlets available for betting.
(The total number of sites is hard to ascertain because of confidentially rules, overlap among city agencies and the number of groups and agencies involved in running sites).
But they said a precise death toll was impossible to ascertain because the army had removed bodies from the stadium where as many as 50,000 had gathered to protest the ruling military junta.
