The phrase "are difficult to validate" is correct and usable in written English.
You can use it when discussing something that is challenging to confirm or prove, often in contexts like research, data analysis, or assessments.
Example: "The results of the experiment are difficult to validate due to the lack of consistent data."
Alternatives: "are hard to verify" or "are challenging to confirm."
Although the presented dollar values are difficult to validate, the model strongly suggests that the three divergent trajectory patterns are valid since the increases and decreases in households represent expanding and contracting economic scenarios adequately.
Large area land cover products generated from remotely sensed data are difficult to validate in a timely and cost effective manner.
Many claim to offer improvements over older designs but such assertions are difficult to validate when there is no consensus as to how such implants should be tested in vitro or even if such testing is necessary.
However, the results presented here are only as good as the population and GDP data on which they are based, as well as the multi-hazard intensity estimation at the grid scale since the availability of global data is limited and the quality of disaster and exposure data are difficult to validate.
However, there are still some pending issues about the accuracy (and validity) of the VHF radar-derived turbulence parameter estimates, because the data processing methods used are difficult to validate and because the VHF radar backscatter mechanisms are complex and still not fully understood (e.g., Röttger and Larsen 1990; Hocking 2011).
Of course, without information concerning the actual structure of the network these notions are difficult to validate.
It is difficult to validate all of these potential biomarkers because each validation requires it own specific and sensitive test, which together is rate-limiting.
During data entry, there are some built-in data validation steps, but despite this it is difficult to validate all of the data entered and we have to accept that there might be some errors.
One possibility for the relatively low confirmation rate of the data from the AD-C library is that the increases in the expression of unconfirmed transcripts were small and, therefore, might also be difficult to validate by qRT-PCR, although this wasn't evident in the qRT-PCR validation of down regulated genes from the C-AD library.
Established sleep researchers say lucid dreaming is occasionally reported by subjects, though it is difficult to validate scientifically.
However, the accuracy of the model was difficult to validate.
