Assuming the relation between test scores and future growth is indeed causal, the OECD study also works out the economic benefits of improving cognitive skills by the equivalent of nine months' worth of schooling.
First, as Dr. Goodall makes pains to point out, this study does not advocate a causal association between physician-led hospitals and their performance.
Study after study has concluded there is no causal link between the reduction in nuisance crimes, like turnstile jumping or aggressive panhandling, and the reduction in serious crimes, like robbery and murder.
The researchers said although a causal effect could not be proven, the way they had done the study strongly suggested that it was exposure to alcohol in the womb that was responsible for the differences in child IQ.