Those are absolute risk reductions, not relative ones. The 1.7 percentage point reduction equates to a 37% reduction in all cause mortality, and a 1.2 percentage point increase is a 25% increase.

Those are huge numbers. The problem is that the confidence interval is really wide.

>but the overall effect is small.

quibble: non significant, wide confidence doesn't mean "small", it means _unknown_. It means the data is too sparse and/or too noisy to tell.

Doesn't this also imply that the effect is "small" even if real? After all if there would be a very strong correlation (eg a true and exclusive casual chain) then we would see a huge signal even in small and noisy datasets. Or am I missing something?

No. If you look closely at the data you might be able to draw such conclusions but lack of statistical significance often doesn't suggest or imply a small effect. Notice that in this case in particular, the confidence intervals are consistent with very large positive or fairly large negative effects. Don't underestimate the amount of noise often found in studies. Lack of significance usually just means that data is too noisy to tell us anything. If you get significance you get to say: the data is probably not pure noise but the effect could still be very tiny or caused by systematic measurement errors. Null hypothesis testing is pretty useless really.

Thanks for your detailed reply! I meant that even this dataset puts a limit on the effect size, if viewed as an "evidence of absence of clear and large effect".

Of course since "everything is correlated" [0] expecting such truly simple signals might be nonsensical/pointless.

I was just lamenting the lack of simple magical treatments basically.

[0] https://www.gwern.net/Everything

That gwern page is excellent!

>Participants were randomised to two sessions weekly of high intensity interval training at about 90% of peak heart rate (HIIT, n=400), moderate intensity continuous training at about 70% of peak heart rate (MICT, n=387), or to follow the national guidelines for physical activity (n=780; control group); all for five years.

I can't quite tell by your summary whether you are saying "exercising is good, but the overall effect on mortality is small", or "exercising is good, and the effect of adding HIIT to baseline exercise is small".

You cannot make the former statement from this study as control group were not non-exercisers (and adherence was decent). The latter statement, does seem to be supported.

Regarding exercise in general, the literature shows the mortality gap between exercisers and non-exercisers is absolutely massive.