The phrase "an additional difficulty is" is correct and usable in written English.
It can be used when introducing a new challenge or complication in a discussion or argument.
Example: "While we have made significant progress, an additional difficulty is the lack of resources available for the project."
Alternatives: "another challenge is" or "a further complication is".
And meanwhile an additional difficulty is that, for Muslims who are disaffected or alienated from society, religion seems to provide a potent, and not necessarily benign, kind of solace.The right response to any group that preaches violence many Islamists do not is to prosecute and ban it.
When residual biomass resources are used, an additional difficulty is that the amount of residues depends on the original product stream, not the demand of the biogas installation.
However, an additional difficulty is the problem of potential simultaneity bias between the REER and (1) trade openness and (2) trade balance, which we have approached by instrumenting both independent variables with their first available lags in a two-step OLS framework, as proposed by Banerjee et al.
Currently, an additional difficulty is given by the possibly nondimensional nature of tumor response to many molecularly targeted agents, while standard response criteria are mainly based on tumor shrinkage.
26 However, an additional difficulty is misclassification arising from the lack of precise coding of the histological subtype of esophageal cancer available in primary care records, which were not available for this study.
An additional difficulty is distinguishing a fixed effect due to age at infection from a time-varying effect that changes as a patient ages.
An additional difficulty was created by the inclusion of new or additional participants between waves (e.g. "booster samples", new members in the household, previous non-responders or drop-outs, or studies adopting a policy of continuous recruitment) and whether they were included or excluded from the denominator.
Additional difficulty is the differential diagnosis with depression.
Additional difficulty is the necessity for all technological steps to be embedded into VLSI manufacturing process or, in other words, meet requirements of CMOS compatibility.
One additional difficulty is the lack of the Galerkin orthogonality which is circumvented with the quasi-orthogonality axiom (A3) in Section 3.5.
The additional difficulty is due in part to the study of polymorphisms that are not causal of the interaction, but only in linkage disequilibrium (LD) with the nongenotyped causal polymorphisms (markers or tags) [ 44].
