Alex,
But in part a we didn't calculate intervals, we
calculated values.
Those values define the intervals. In 3a you are asked to calculate
the 99, 95, and 80% intervals. That is, the values between which, for
example, 99 percent of the normal density with mean 0.05 and variance
26 should be. In part 3b you are asked to calculate what proportion
of changes in approval are actually within the bounds calculated in
3a.
See the bottom of
http://jsekhon.fas.harvard.edu/gov1000/normal1.R for
an example.
JS.
Alexander Liebman writes:
Hi,
Quick question about 3b. It asks us to compare the percentage of actual
changes in presidential approval with the "intervals we just calculated [in
part a]." But in part a we didn't calculate intervals, we calculated values.
I see how to do the problem by comparing it to what the percentages should
be, so I just want to make sure that this is what we're supposed to do.
Thoughts?
Alex