The phrase 'difficult to be assessed' is correct and usable in written English.
You can use it when you need to describe something that is challenging to measure or evaluate. For example: "The effectiveness of the program is difficult to be assessed due to the lack of available data."
An analytical model is also proposed to predict the adhesion stress and to support the wavelet analysis technique where the stress is difficult to be assessed.
Although we performed not only Pearson x2 analysis but also a multiple linear regression analysis in the previous study, neurological function is difficult to be assessed for the patients with multiple injury levels.
These factors are sometimes difficult to be assessed and quantified accurately and their actual influence on body fat variation might not be judiciously accounted for in statistical analyses, although there is a debate on whether the statistical adjustment for environmental factors is necessary [39].
All these contextual factors may contribute to suicide risk, but for each individual patient, they are difficult to be assessed objectively and consistently without a proper tool.
Perception on teamwork is difficult to be assessed with a questionnaire and the self-administered nature of it could also be considered as a limitation.
It is possible that the effect of diabetes becomes more evident as AAAs increase in size which was difficult to be assessed in this study because most of the AAAs were <4 cm.
Early partial response to radiosurgery is difficult to be angiographically assessed in a reliable manner.
Papers that were difficult to assess were additionally reviewed by GR and MS, then jointly assessed.
As a result, it is difficult to assess what is going on with the population as a whole.
Although Barzun's influence on literary studies is difficult to assess, there's little doubt about his role in the revival of Hector Berlioz.
It's difficult to not be cynical when assessing any reforms that this Conservative government rolls out.
