This was a tricky question - larger tumor is more likely to be detected by any self breast exam especially if the breast tissue is less dense or small (in comparison to smaller tumor lesion). Regarding the bias component, you can then make the argument that because it is larger lesion it is detected earlier (could be tracked longer and thus give impression of longer 5-year survival), but maybe larger lesion also translates to worse prognosis (faster growing, less indolent course) in which case one can make the argument that these patients die earlier, leading to shorter survival.
Hi, Mignote!
Thanks for asking. I think you are making this harder than it needs to be. Here's a hint: you can assume every tumor detected at >= 2cm was once a tumor < 1 cm, and for this problem you can ignore that this was an RCT of BSE.
Best wishes,
Tom