The Brown Bear & The National Margin (Part Two)

In this post the Brown Bear explains how he calculates the Presidential Job Performance portion of the National Margin.

As an example, let's consider the polls results released by Time & Newsweek a week ago. For Time, the results were 53% approve, 44% disapprove; for Newsweek, the results were 46% approve, 47% disapprove. The Brown Bear first calculates the undecided vote by adding the approve and disapprove numbers for each poll and subtracting the result from 100%. For Time, the undecided is 100% - (53% + 44%) = 3%; for Newsweek, 100% - (46% + 47%) = 7%. The Brown Bear then calculates the Adjusted Job Performance Rating for each poll by adding one-third of the undecided result to the approve result. For Time, the Adjusted Job Performance Rating is 53% + (3% ÷ 3) = 54%; For Newsweek, it is 46%+ (7% ÷ 3) = 48.33%.

The Brown Bear then calculates the age and weight of each poll in the manner described in The Brown Bear & The National Margin (Part One). For Time the age and weight of its poll were 50 and 141.323; For Newsweek, the age and weight of its poll were 51.5 and 163.953. (Remember that the older the poll the smaller the age. In our example the Time poll is older.) The Brown Bear then multiplies each poll's Adjusted Job Performance Rating by its weight to obtain a Weighted Rating. For Time, the weighted rating is 54% x 141.323 = 76.315; for Newsweek, it is 48.33% x 163.953 = 79.244. The Brown Bear then adds all the weighted ratings for the polls he is considering. For Time & Newsweek, this sum is 76.315 + 79.244 = 155.559. The Brown Bear then divides this sum by the sum of the poll weights (for Time & Newsweek, this sum is 141.323 + 163.956 = 305.277) to obtain the Presidential Job Performance Rating. For Time & Newsweek, this result is 50.96% (155.559 ÷ 305.277 = .5096).

The Brown Bear then combines the Presidential Job Performance Rating with the National Poll Margin which was described in Part One to obtain the National Margin. First, the Brown Bear takes the National Poll Margin and adds to it the 3^rd Party Percentage (currently at 1.8%). For the Time & Newsweek polls, the National Poll Margin was 3.39%; 1.8% + 3.39% = 5.19%. The Brown Bear then divides this sum in half. For the Time & Newsweek polls, 5.19% ÷ 2 = 2.595%. The Brown Bear then takes the Presidential Job Performance Rating and subtracts 50% from it. For our example, 50.96% - 50% = 0.96%. The Brown Bear then adds this result to the previous result to obtain the National Margin. For the Time & Newsweek Polls, 2.595% + 0.96% = 3.55%.

The Brown Bear calculates the percentage of the vote for each candidate that he posts in his daily updates in the following manner. He takes the 3^rd Party Percentage and subtracts it from 100%, obtaining the Two-Party Percentage; 100% - 1.8% = 98.2%. To obtain the leader's percentage he adds to the Two-Party Percentage the national margin and divides the resultant sum in half. In our example using Time & Newsweek polls, this result is (98.2% + 3.55%) ÷ 2 = 50.87%. To obtain the percentage for the candidate trailing the race, the Brown Bear subracts the national margin from the Two-Party Percentage and divides the result in half. For the Time & Newsweek polls this is (98.2% - 3.55%) ÷ 2 = 47.33%. Therefore, using The Brown Bear's method on just the Time & Newsweek polls from last week, the result would be George Bush 50.87%, John Kerry 47.33%.