I am confused, again (updated)

According to this news report:

A new study by Canterbury University's GeoHealth Laboratory showed fast-food outlets were 5 1/2 times more likely to be clustered around schools than other areas and three times more likely to be in poorer areas than rich.

and

Day studied the clustering of fast-food and convenience stores around schools in Christchurch, North Shore, Waitakere, Lower Hutt and Wellington.

So do fast-food outlets cluster around schools or do schools cluster around fast-food outlets or is some other factor causing the clustering? An example of the last point would be that both schools and fast-food outlets occur in areas of high population density. And how did the researchers check for causation?

And as for the fact that fast-food outlets more likely to be in poorer areas than rich, could this be because their food is cheaper? 5-star restaurants in poor areas may be nice but it seems unlikely that there would be enough demand to keep them going.

And if there is a "childhood-obesity epidemic sweeping the Western world" (proof?) whose job is it to bring up the kids with sensible eating habits? The fast-food manger or the parents? The problem here may not be the distribution of fast-food outlets but rather the parents teaching of their kids.

Update: Kiwiblog comments here, Eternal Lacking here. This comments makes the point that may be rents are lower in poor areas which may attract fast food type business.