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According to Wikipedia,

A "blunt" support curve (one with a shallow maximum) would have a low negative expected second derivative

In my mind, a blunt support curve has slow-changing slope, hence small second derivative, hence big negative expected second derivative (instead of small).

Where am I wrong in my thinking?


marked as duplicate by kjetil b halvorsen, mdewey, Michael Chernick, Robert Long, Peter Flom - Reinstate Monica Aug 31 at 10:43

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  • $\begingroup$ Expected second derivative is an average. If you average small things, they are still small. Why do you think they become big? $\endgroup$ – mpiktas Jan 29 '16 at 7:24
  • $\begingroup$ It's because of the negative sign, not because of the expectation. $\endgroup$ – Heisenberg Jan 29 '16 at 7:25
  • 2
    $\begingroup$ Well the second derivative is negative around the maximum, see en.wikipedia.org/wiki/Derivative_test, why do you fixate on its size? $\endgroup$ – mpiktas Jan 29 '16 at 7:33
  • $\begingroup$ Ah! That's what I missed. I knew it would be something straightforward like that. If you want to post an answer, I'll accept it. $\endgroup$ – Heisenberg Jan 29 '16 at 7:40