A new CNN/Opinion Research Corporation poll taken 8/18-20/06 finds approval of President Bush continuing to rise, with approval now at 42% and disapproval at 57%. That is a 2 point rise in approval and a two point decline in disapproval since the last CNN/ORC poll 8/2-3. With the addition of this data point, my approval trend estimate stands at 37.2%, revised up from the previous 36.7%.
But hold on a moment. The new CNN is an outlier-- as was the AP's reading of 33% on 8/7-9, in the opposite direction.
An outlier is a poll result that is unlikely to occur, given the current estimate of the overall trend, which was 36.7% prior to the new CNN poll. That means CNN at 42% is 5.3 points higher than we would expect. Over the nearly 1200 polls taken in the Bush administration, 90% fall within -4.7 and + 4.0 percentage points of the estimated trend, with 5% of polls below -4.7 and 5% of polls above +4.0 points from the trend. At +5.3, the new CNN clearly is above the upper limit. Now that CAN happen by chance alone (and WILL, 5% of the time, by definition) and it could also signal a sudden and abrupt shift up in approval, though the lack of an obvious reason for such a shift makes me think not. What highlighting outliers does is caution us not to place too much confidence in a single outlier. Just as some Dems were delighted by the AP at 33%, now some Reps will be thrilled to see CNN "validate the President's improving ratings". Neither is likely to be supported by further polls, nor by shifts in the trend estimate. Outliers happen, but they rarely signal true change.
Based on this, I expect the approval trend is more accurately represented by the 36.7% we estimated prior to this CNN poll. A couple more polls within the expected range will bring the estimated trend back towards that level.
Even with the CNN outlier, the trend estimate remains slightly down, which is probably the more important harbinger.
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