In the excellent article “Beware the
long tail” (SN: 11/5/11, p. 22), the areas
under each curve in the figure “Spot-
ting the tail” should be unity (the total
probability must be one). Therefore,
the red curve should be lower in the
center than the black one.
Filson Glanz, Durham, N.H.
Yes, the area under each curve should
add up to one. In this case the graphic
was shown without a y-axis to illustrate
the basic point about the shapes of
such curves; it would have been more
appropriate to have shown the curves
separately rather than superimposed.
— Rachel Ehrenberg
The graphic “Event prediction” shows
the Shanghai Stock Exchange Composite Index starting to decline at the
beginning of the predicted period (gray
bar) in 2009, but the text states that the
bubble burst July 29, two days after the
prediction of July 17–27. What is the
Bobby Baum, Bethesda, Md.
The graph was reproduced from a
paper in the Journal of Economic
Behavior and Organization, which
misplaced the gray bar for the 2009
prediction. The bar should have been
farther to the left, such that the gray
area ends right before the index’s fall.
— Rachel Ehrenberg
Standardizing the boom
I read your article “Explosive goes
boom, not too soon” (SN: 10/22/11,
p. 10) and had to wonder, why 2,940
grams for the drop test weight? It
certainly doesn’t convert to a straightforward number of pounds or ounces.
Paul Johnston, Kamuela, Hawaii
Materials chemist Adam Matzger of the
University of Michigan in Ann Arbor
replies: “This is the weight of the 3.5-
inch steel drop weight we used. It is not a
standard size; in fact, there is not really
a standard, so we calibrated our drop
weight system against established
The research that concludes kids are
generous and chimps are not (“Kids
share, chimps stash,” SN: 8/27/11,
p. 10) based on two dissimilar studies
makes no sense to me. The children
were sharing marbles, the chimps food.
Ask a bunch of hungry 3-year-olds to
share chocolate chip cookies and see
what happens. Then, if they do share, I
might believe the children are altruistic
and the chimps are opportunistic.
Eleanor K. Summer, Gainesville, Fla.
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