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For flag variables, values of only "Y" or null are used when a value of "N" is unimportant to the analysis (i.e., "N" and null are treated the same in the analysis). Flag values of "Y", "N", or null should be used when "N" and null are treated differently in the analysis. The values shown in the Codelist/Controlled Terms column support common statistical needs. If required, the codelist/controlled terms values can be changed from "Y" to "Y, N".