In reply to Ken Kleinman.

I don't have expertise in block randomization. My first thought would be to look at PROC PLAN.

I discussed this with a colleague. We think that "assignments are made sequentially" refers to the investigator applying the block randomization assignments to subjects. When the block size is fixed (with fixed treatment/placebo allocation) and the process is non-blinded, then the investigator will know what the final assignment(s) in the block will be. I think this concern is sometimes addressed by using a blinded process or varying block sizes.

I don't think Ken's comment refers to a sequential selection method (e.g., Chromy's method).

PROC SURVEYSELECT does not provide an option with GROUPS= to discard the first N units/assignments in each block (stratum or replicate). But you could do this in a separate DATA step.