The phrase "are frequently substantial" is correct and usable in written English.
It can be used to describe something that often has a significant or considerable impact or importance.
Example: "The findings of the research are frequently substantial, leading to important changes in policy."
Alternatives: "are often significant" or "are regularly considerable."
Identification of visual field loss in people with retinal disease is not straightforward as people with eye disease are frequently unaware of substantial deficits in their visual field, as a consequence of perceptual completion ("filling-in") of affected areas.
Hazards to health, offenses to the sense of smell or hearing, and demonstrated economic loss are frequently found to be substantial harms.
For example preclinical studies are frequently small and there is often substantial heterogeneity between studies.
This is the case in healthcare, particularly in commissioning decisions which are frequently criticised due to the substantial variability observed across England.
While durable complete remission remains an elusive goal in the treatment of AIPC, substantial responses to therapy are frequently reported.
CH patients are frequently diagnosed with sinus or dental problems, and many experience substantial delay in receiving a diagnosis [8 10].
Gout therefore represents a condition of the aging population where effective management can be frequently complicated by substantial comorbidities.
CRPS is frequently associated with substantial disability, loss of quality of life and personal and societal economic burden.
In order to avoid circular and inconsistent relationships, the continuous Bass Model has been modified in different discrete versions even in the original Bass paper [17] (although that version is frequently referenced it introduces substantial error into the model).
At least among linear measures the relationship is frequently allometric, resulting in substantial variation in the extent of polymorphism among structures, including complex variation associated with sigmoidal or discontinuous static allometries, such as found in beetle horn polymorphisms [18], [39].
