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North Carolina: Trend Sensitivity

Topics: 2008 , Barack Obama , Hillary Clinton , Rasmussen

Time for another update looking at the "sensitivity" of our trend lines for North Carolina. As Professor Franklin is tied up with his day job this morning, I will be your guide. But let's go immediately to the chart that Franklin just generated.

The solid red and blue lines represent our standard trend estimates of support for Barack Obama and Hillary Clinton, respectively, in North Carolina. The trend lines are based, not on simple averaging, but on a local-regression based trend. We deliberately set the standard estimate to be conservative in that it takes a good bit of evidence of "real" change (i.e. more than one or two contrary polls) before the trend will show a sharp turn. As we have noted before, with lots of polls, this more conservative estimator has an excellent track record of finding real turning points of opinion while not chasing outliers.

In this case, however, the standard line appears to be too conservative. The last nine polls have produced results below the solid trend line for Obama and all but one above the trend line for Clinton. So in the graph above, we have also included trend lines based on a more sensitive estimator -- the dotted lines -- for both candidates. The sensitive estimator uses the same local regression methodology as our standard approach, but sets the degree of smoothing to about half that of the standard blue estimator. The sensitive estimator should detect short term change more quickly than "blue", but it will also sometimes chase phantom changes due to flukes of a few polls that happen to be too high or too low.

In this case, for the moment at least, the sensitive estimator (which shows Obama leading by a 7.7 point margin or 50.3 to 42.6) fits the most recent data better than the standard estimate (which shows Obama leading by 13.7, or 52.7 to 39.0).

Update: In the hour since Charles generated this chart, we have added new polls from Rasmussen Reports and ARG that change the numbers for the standard estimates on on our North Carolina chart slightly from what appears in the graph above. We'll try to post an update of the more sensitive estimate trend later this afternoon.

 

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