The phrase "a frequent difficulty of" is correct and usable in written English.
It can be used to describe a common challenge or problem associated with a particular subject or situation.
Example: "A frequent difficulty of learning a new language is mastering the pronunciation."
Alternatives: "a common challenge of" or "a regular issue with".
Furthermore, a frequent difficulty in assessing the clinical value of prognostic markers is the relatively small number of patients in primary research studies, sometimes a consequence of disease rarity and limited resources, such that each primary study has low statistical power for detecting any benefits of prognostic staging.
The streak of craziness; the thrill of the quest; the frequent difficulty of describing what their invention was, how it worked, what it was for; their vulnerability to ridicule, because what they had done or thought was new; and the need to protect that thought, as something interesting and precious in itself.
Much remains to be learned about molecular alterations and gene expression patterns in primary tumors versus their metastases, but these studies are complicated by the frequent difficulty of obtaining matched tissue samples, especially when metastases may be detected long after a primary tumor has been resected.
Given the drama of the phenomenon of sexual assault/abuse against women and minors and the frequent difficulties of interpretation, the international Scientific Societies have found it necessary to develop guidelines for the investigation of suspected cases of sexual violence.
Over lands, the cloud detection on remote sensing images is not an easy task, because of the frequent difficulty to distinguish clouds from the underlying landscape, even at a high resolution.
Lymph node cases usually represent a frequent source of difficulty and specific details have to be provided in submitting such cases.
Memory problems were investigated by the self-reporting of frequent difficulty with remembering recent events in the last 12 months dichotomously.
The major and frequent difficulty in expressing a heterologous protein in a bacterial system concerns the tendency of the recombinant protein to become insoluble [ 17].
Montreal respondents were also more likely to report a decline in their standard of living and more frequent difficulty making ends meet than those in the other two cities.
The owner had to describe at least three of the following signs as being frequent: difficulty in lying down and/or in getting up from a lying position, difficulty in jumping or refusing to jump, difficulty in walking up or down stairs, or definite lameness.
