How assay of API decrease with moisture content is there any trend or authentic reference?

Is there any specific trend or graph at which assay of API decrease with moisture content?

Assay of API is inverse proportional to the moisture content.
i.e; weight of the sample varies due to the presence of M.C in API.
Ex: 1) If API having M.C about 3.0%, then the obtained assay result is considered as is basis.
2) In assay calculation formula, if we subtract the M.C then the obtained result is considered as anhydrous basis…
From the above two cases, you can get different assay result for the same API.