For one thing, the large improvement in ionic conductivity will require further verification, Wachsman says, especially in light of the difficulty of measuring the performance of extremely thin materials.
Another challenge with in vivo measurements is the difficulty of measuring enzyme and intermediate enzyme complex concentrations [ 7, 8], so these are typically unknown.
This absence of evidence in spite of strong clinical belief in the efficacy of co-activation is likely due to the difficulty of measuring in-vivo tibial translation or ACL elongation while performing a dynamic task.
In his article about the difficulty of measuring online audiences ("But Who's Counting?" March/April 2009), Jason Pontin made the case that media companies, and the advertisers they wish to attract, need better tools for measuring how many people are visiting their sites.
While process design in biotechnology often rests on the relationship between microbial yield and the degree of reduction of the substrates, microbial ecologists have not used this relationship frequently, at least in part, because of the difficulty of measuring the elemental composition of DOC [60].
The proteins and genes for all plastid transport proteins may not have been identified yet, in part because of the difficulty of measuring transport by membrane proteins to verify their function.
A key problem that has faced those in this field in the past has been the difficulty of measuring motivation using psychological tests and questionnaires.
In conclusion, this comparison suggests confidence in the 5S measurements, but also illustrates the difficulty of measuring the repeats.
Although structures and processes are imperfect surrogates for outcomes, they are used frequently in P4P programs because of the difficulty of measuring and risk-adjusting outcomes [ 26].
