Table 1.

Common methods of masking tissues for histopathologic examination.

Method	Description	Comments
Comprehensive	Individual samples are labeled without reference to treatment group (e.g. 1, 2, 3, 4, 5, etc.) and minimal background information (perspective) is given.	Pro: Bias is comprehensively constrained Con: Pathologist labor may be increased in examination, while sensitivity to subtle study-specific lesions may decrease12
Grouped	Samples are coded by groups (e.g. A1, A2, …A10; B1, B2, ….B10); relevant background material including study design and objectives are disclosed to pathologist.	Pro: Pathologist is masked to group treatments, but is aware of tissue grouping and background information. Con: Overt group differences can functionally unmask the pathologist and if performing ordinal scoring may warrant comprehensive masking.
Post examination masking	Full disclosure of experimental design and objectives with unmasked initial evaluation; masking and randomization of samples are done prior to scoring	Pro: Offers full disclosure to the pathologist for examination and scoring development. Con: Pathologists may recall group assignments of samples with small n/group which makes masking ineffective.