Sunday, February 19, 2006
two points for my manifesto
1. There is no such thing as a "direct effect" of education on a later-life outcome, and thinking that way only leads to confusion. As far as I can tell, all coherent narratives of the effect of education on a later-life outcome can be expressed in terms of the above diagram.* The way people talk about education "effects" would be clearer if people were forced to express what they think they mean in terms of this diagram.
(Note that the diagram does not have an arrow that goes directly from education to the outcome; that's a big part of the point. The diagram may seem obvious or banal, but I can point to about 1000 confused papers that I've read that would have benefited by being forced to be clear of what they are claiming in exactly the terms above.)
2. As a general thing, people overestimate the extent to which education "effects" result from processes carried along the yellow arrow. They underestimate the spurious relationship borne along the blue arrows, and the true causal effects of education that proceed through the red arrows. The spurious relationship borne by the green arrows, I think, variously and weirdly ends up being both overestimated and underestimated.
* Adding the proviso that any instances of two arrows entering a node allow for the possibility of 'interaction effects' and where person-situation casuation both earlier and later in life can be more 'dynamic' than what is strictly depicted in this diagram.