> I should be able to state that two species have a different lifespan based on a difference in mean age of death - without needing to provide any specific biological mechanism in my study.
You need to control for confounders. For example, if I told you:
- Mean lifespan of species 1 is: 3 years
- Mean lifespan of species 2 is: 10 years
Does that mean that species 2 has a longer lifespan than species 1?
What happens when you find out that species 1 is domesticated cattle, which has (almost) all of its males slaughtered at age 2?
You could then say "I meant for two species that are in controlled conditions", but now you need to define what conditions you're controlling, which implies what casual mechanisms you're controlling for.
> which implies what casual mechanisms you're controlling for.
Without thinking terribly deeply about it, it seems like this could be modified to
"what correlated mechanisms we're controlling for", in which case, yes I think if we controlled for the highly correlated variable of "does this cow live on a meat farm" with the mean age, we would be able to make broad claims about cattle lifespan without needing to be privy to the internal mechanisms of the agriculture industry
You need to control for confounders. For example, if I told you:
- Mean lifespan of species 1 is: 3 years - Mean lifespan of species 2 is: 10 years
Does that mean that species 2 has a longer lifespan than species 1?
What happens when you find out that species 1 is domesticated cattle, which has (almost) all of its males slaughtered at age 2?
You could then say "I meant for two species that are in controlled conditions", but now you need to define what conditions you're controlling, which implies what casual mechanisms you're controlling for.