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Thank you for pointing this out, Tom. The x-axis is indeed mislabeled. It should simply be 'Year' and not 'Year of diagnosis'. These labels are added automatically when you generate the graphs on the WHO/IARC web site (see: gco.iarc.fr/en) but I should have caught it myself before posting of course. There is a lot of interesting data on there to play around with. You should try it out!
Best
Karsten
Thank you for pointing this out, Tom. The x-axis is indeed mislabeled. It should simply be 'Year' and not 'Year of diagnosis'. These labels are added automatically when you generate the graphs on the WHO/IARC web site (see: https://gco.iarc.fr/en) but I should have caught it myself before posting of course. There is a lot of interesting data on there to play around with. You should try it out!
Best
Karsten
Still not sure I follow. How does figure 1 show greater benefits for younger women? The absolute mortality difference is not smaller in this group. Is this based on RRs? If so how is this justified?
If you look at the decline in breast cancer mortality over time in figure 1, it has been largest in the youngest age group, from about 20 to 12 per 100,000 women, or a 59% reduction) and reductions are getting gradually smaller in older age groups (for example from about 110 to 62 per 100,000 women aged 65 to 69 years, or a 53% reduction). In Canada (data from which the graphs depict), younger women have generally been screened far less than those aged 50 to 74 years. If breast screening was the main cause of declines, we would expect the largest reductions in age groups most likely to benefit. But universally, declines have been largest in younger women, regardless if they have been screened or not. This fits with all age groups having access to improved therapy and younger women benefitting more, not with screening being a major contributor this this incredible success story.
Thank you. But my question was what justifies using relative risk reduction instead of absolute risk reduction to claim an age-related benefit?
Any risk reduction has to be seen in relation to the base risk. The RR reduction is not meaningful unless you know the base risk, which is what I think you refer to? The base risk is of course much, much lower in younger women. So, even if the relative risk reduction (or percentual risk reduction) is greater in younger women, the absolute risk reduction might be larger. However, when we compare effects between age groups, it is the differences in relative risk reductions we need to look at. Did that answer your question?
I was confused, I apologize. What I’m not clear on is how you relativized the data. If mortality rates aren’t normalized by age group, you cannot meaningfully compare them. From the description of figure 1 I cannot tell whether that has been done. Can you clarify?