Times Jumbo Cryptic No 836

[Mikejas]

38a Carefully mark one answer gone through outside---that's fair (8) ?N?I?S?D ( I think it's UNBIASSED but can't work out the rationale.)

[Mysterons]

Unbiased

'carefully mark' = nota bene (nb)
'one answer' = ia

[Mikejas]

Thanks mysterons. As usual it seems so simple when someone else explains