I can’t imagine what you are thinking of – please see page 61 of the notes. If a subsidiary is material, it will be audited – so you can’t be thinking of sampling risk. I suppose there could be non-sampling risk if the group auditor used inappropriate procedures because they were not sufficiently competent in auditing a group of companies – but it would make no difference whether it was a 50% subsidiary or 100% or something in between.
And please give your posts more information titles to help your fellow students use the search feature – e.g. Group audit – detection risk