Yesterday, Gallup reported a big jump in their three-day rolling average of President Obama’s approval rating. Can we figure out what day it happened? Yes, and it shows how a single speech can move national opinion, even if only briefly.
The last few individual data points plotted above (downloadable) look like this.
In boldface is the post-DNC bump. This is quite notable: the last time the approval number went as high as 49% was June 9-11. This suggests that something happened to drive the numbers up suddenly on September 4th, the night of Michelle Obama’s speech.
Is this even possible? Michelle Obama’s ratings were through the roof. Nielsen estimated the viewership at about 50 million people, outstripping the entire RNC convention. Her speech went viral in China, providing independent verification of her broad appeal. Could it be that a significant fraction of US viewers improved their opinion of Barack Obama after hearing her?
Gallup does not release its single-day numbers. Mathematically, it is impossible to extract a unique set of one-day numbers from a rolling average. However, it is possible to surmise the likeliest set of numbers by adding one assumption.
Opinion is unlikely to fluctuate massively from day to day. We can calculate the set of one-day values that fluctuates the least from day to day. This assumption is easily implemented using an algorithm for variance minimization (MATLAB code here). Here is the result:
From Sept. 4th to Sept. 5th-6th, a total swing of 16-17 points occurred. The United States has approximately 240 million citizens of voting age, so this means that a net 20 million people were flipped during that period. Evidently Michelle Obama was extremely persuasive, and maybe Bill Clinton too. But judging from the swing back on Sept. 7th, President Obama could not quite sustain the impact of the first two speakers.
There’s a chance that the “unrolling” process did not get things quite right, and Obama’s boost was actually sustained. If the Gallup 3-day average approval comes down to 49% in today’s release, we’ll know that the bump was a short-lived one. We will find out soon.
One imagines that the Obama campaign is planning to deploy the First Lady’s speech in more markets.