Sometimes, even the number of species present may be difficult to ascertain.
White added that it would also be difficult to ascertain the precise details of a helicopter's intended flight path.
It may sometimes be difficult to ascertain whether a transfer of copyright is voluntary or is coerced by covert pressure.
But munitions that are produced in one country are often copied by manufacturers in another, so it can be difficult to ascertain a weapon's point of origin.
This is because it may be difficult to ascertain whether wanting to be a girl is merely a passing game, or something that won't leave him.
Once one avenue of inquiry is closed off, it can be difficult to ascertain what happened along other points in the mortgage chain.
This is all the more important where terrorism and security are at issue because facts can be difficult to ascertain, even where they pose absolutely no risk to national security.
The inclusion of complexity measures such as tooth loss due to periodontitis and alveolar ridge defects, which may be difficult to ascertain and/or may not be well defined.
The only relevant domain identified by most guidelines and textbooks was a lack of response or a loss of effectiveness, both of which can be difficult to ascertain in the course of a progressive condition.
The difference in patient-reported outcomes between study arms can often be difficult to ascertain in randomized controlled trials (RCTs) using a parallel design because of wide interindividual variations in baseline characteristics and how patients interpret the outcome measures.
End groups play a critical role in macromolecular coupling reactions for building complex polymer architectures, yet their identity and purity can be difficult to ascertain using traditional analytical technique.
