The phrase "and difficult to demonstrate" is correct and usable in written English.
It can be used when discussing concepts, theories, or phenomena that are challenging to prove or illustrate.
Example: "The theory is complex and difficult to demonstrate, making it hard for many to grasp its implications."
Alternatives: "and hard to illustrate" or "and challenging to prove".
However, the relationship between language proficiency and international students' academic success is complex and difficult to demonstrate, and the results from previous studies are mixed and highly inconclusive (Cho & Bridgeman, 2012).
Previously, it has been reported that Leishmania parasites are scanty and difficult to demonstrate in skin lesions with macular/papular presentation [29].
It has been hypothesized that free radical damage in the aging brain causes inflammation [ 18] but free radical damage in neurons is subtle and non-specific, and therefore difficult to demonstrate histopathologically in normal human brain [ 49].
The significance of pedagogy in teaching assistant #1's sections presents a very important observation that is intuitively obvious and methodologically difficult to demonstrate.
However, possible bone toxicity of long-term, low-dose MTX treatment in humans remains a matter of debate and is difficult to demonstrate in cross-sectional [ 36, 37] or longitudinal studies [ 38].
Such an effect of 5%to10%0% is similar to the test-retest variability of molecular imaging techniques using PET and SPECT [20 22] and may be difficult to demonstrate in PET and SPECT studies using small data samples.
The relationship between phenomena such as stigmatisation and human health is complex.69 Whilst there are certainly links between stigmatising situations and harms to human health, they may not always be apparent and may be difficult to demonstrate in reality.
In fact, the differential effects of IFNα and IFNβ are difficult to demonstrate.
This complexity makes an unequivocal relationship between stress and breast cancer difficult to demonstrate using epidemiologic methods.
Thus, local ventricular enlargement appears primarily related to diffuse cortical volume loss, and it is difficult to demonstrate a localized effect on adjacent white matter volume or its anisotropy.
A potential paraneoplastic link between malignancies and glomerulonephropathies is difficult to demonstrate, but is supported in our patient by the parallel improvement and longterm resolution of the two conditions under treatment.
