The phrase "a difficult evaluation" is correct and usable in written English.
It can be used when referring to an assessment or judgment that is challenging to make or requires considerable effort to complete.
Example: "The project required a difficult evaluation of the risks involved before proceeding."
Alternatives: "a challenging assessment" or "a tough appraisal".
A decade later they would become the largest single export customer, with a $1 billion order for the aircraft in 1978, the Jaguar being chosen ahead of the Dassault Mirage F1 and the Saab Viggen after a long and difficult evaluation process.
As a former policeman, Kalivoda had passed a difficult psychological evaluation as part of the police selection procedure.
Such heterogeneity renders the inner nature of the aging process of difficult evaluation in older persons due to the potential biases introduced by multiple age-related social, biological, and clinical factors (and responsible for the evidence-based issue in geriatrics).
The faint bands on DGGE gels are of difficult evaluation and often ignored [3, 10, 18, 19], while sequencing of the intense bands has sometimes revealed the presence of more than one species [10].
In humans, the limited number of patients as well as the heterogeneity of the procedure led to the difficult evaluation of the efficiency of the different treatments.
The determination of safe weld excavation sizes for repair is one of the more difficult evaluations in pipeline installation engineering.
They show that the United States has imprisoned hundreds of men for years without trial based on a difficult and strikingly subjective evaluation of who they were, what they had done in the past and what they might do in the future.
Third, ratings are a difficult cognitive task, requiring evaluation of the intensity of preference on a predetermined numerical scale [14].
In the study of melphalan it is important to recognize that the remission status is a difficult end point for evaluation as it is also influenced by an effect of the induction therapy and maintenance.
In Things to Come, Isabelle Huppert plays Nathalie, a long-tenured philosophy teacher at a Parisian university whose comfortable existence gets upended by the revelation of her husband's adultery and leads her into a difficult process of self-evaluation.
