This is an amazing chart — sad in one way, but uplifting in another, because it shows how stats-informed public policy can make a difference.
The chart represents the incidence of SIDS (“crib death”) in Norway plotted out against the rise and fall of parents that put their children to sleep on their stomach. (Which was what they told you to do for a long time).
As you can see, there was not only a correlation of SIDS rate with the rise of prone sleeping, but the public campaign in 1990 that stopped parents from placing children in the crib face-down seems to have had immediate impact on SIDS incidence. While this is never conclusive by itself, this sort of large change in a trend, combined with the roll out of a reasonably related public policy change, is one of the things we look for in a longitudinal analysis.
From Epidemiology and Demography in Public Health (ed. Japhet Killewo):
The distribution of the information that prone (facedown) sleeping was a serious risk factor had a dramatic effect.
In Norway, this information was spread by the mass media in January 1990. The SIDS rate in Norway dropped from 2.0 per 1000 in 1988 to 1.1 in 1990. In a retrospective study, it appeared that the prone (face-down) sleeping position after having continuously increased from 7.4% in 1970, was reduced from 49.1% in 1989 to 26.8% in 1990 (Irgens et al., 1995) (Figure 21).The example again illustrates how important it is to provide scientifically convincing evidence, pivotal to bring results of epidemiological research into practice.
The SIDS experience raises important questions with respect to the reliability of recommendations given to the public based on epidemiological studies. The prone sleeping position had been recommended by pediatricians since the 1960s to avoid scoliosis as well as cranial malformations. Even though a case–control study in Britain early on in the period had observed an increased relative risk, no action was taken; again an example of the necessity to convince scientifically.
Again, just unbelievably sad that so many infants died unnecessarily, but wonderful that a public information campaign saved so many post-1990/