Many of the causal links are obvious.
To be clear: Those are correlations, not causal links.
One of the trickiest things about PISA is making causal links between specific policies and changes in countries' scores.
Understanding any causal links between changed levels of atmospheric greenhouse gases and extreme weather events is obviously of major importance.
"Later on, in the fullness of time, you gradually come to understand the causal links," he told me.
Once we get numbers like those Mr. Brooks trumpets, we need to ask the students themselves about the causal links.
Joblessness is also associated with some serious illnesses, although the causal links are poorly understood.
Their public utterances are generally few and obscure, and the causal links between monetary policy and the performance of the economy are unclear.
In my view, there are two major difficulties with drawing direct causal links between media images and forms of social behaviour.
Campaigners say it is impossible to draw definitive causal links between the fall in deaths and the increase in rescue operations.
In the current environment, attributing low student performance to teacher tenure is one of the great unproven causal links out there.
