The Brown Bear and State Polls

In this post, the Brown Bear will describe how he calculates an average of state polls and how he combines the state poll margin with each state's Degree of Partisanship to determine a final state margin.

As an example, we will use the state of Iowa. The Brown Bear first examines the range of dates a poll was conducted and calculates its Age and Weight (in the same manner as the Brown Bear used in calculating the National Margin). The Brown Bear then for each state chooses the seven polls with the heaviest weights. The Brown Bear then calculates the margin for each poll by subtracting the Republican percentage from the Democratic percentage. The Brown Bear then multiplies each poll's margin by each poll's weight to obtain each poll's weighted margin. The Brown Bear then adds the seven weighted margins of each state and divides the resultant sum by the sum of the weights to obtain the State Poll Margin for each state.

The following chart shows this calculation for the state of Iowa. Remember that a positive margin is a Kerry lead, a negative margin is a Bush lead. In the chart, A is Age, W is Weight, WM is Weighted Margin, P is Pollster, M is Margin.

P A M W WM

SV 56 -3% x 256.00 = -7.68

DM 57 3% x 282.65 = 8.48

Z 57.5 3% x 296.99 = 8.91

MD 58 -5% x 312.07 = -15.60

G 58.5 0% x 327.91 = -6.56

SU 59 -2% x 344.55 = 0.00

F 60.5 -4% x 399.72 = -15.99

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2,219.89 -28.44

State Poll Margin is -28.44 ÷ 2,219.89 = -1.28%

Thus the Brown Bear would conclude that President Bush is leading Senator Kerry in Iowa according to the state polls. For Iowa, the pollsters are, Des Moines Register, Fox News, Gallup, Mason-Dixon, Survey USA, Strategic Vision, and Zogby.

To combine the state poll margin with the historical margin calculated in the previous post, The Brown Bear and Historical Data, the Brown Bear assigns the historical margin an age equivalent to the present date (as if the poll were conducted entirely today). The Brown Bear then calculates the weight for the historical margin in the usual manner (as detailed in the post, The Brown Bear and the National Margin (Part One). The Brown Bear then multiplies the historical margin by the weight assigned to it to obtain a weighted historical margin. For our example of Iowa, the historical margin was -1.54%; today's date is November 1, which yields an Age of 62 and a corresponding Weight of 463.73. Iowa's weighted historical margin then is -1.54% x 463.73 = -7.14. The Brown Bear then adds the weighted historical margin to the sum of the weighted margins obtained from the state polls. For Iowa, this is -28.44 + (-7.14) = -35.58. The Brown Bear then adds the weight assigned the historical margin to the sum of the weights of the state polls. For Iowa this is 463.73 + 2,219.89 = 2,683.62. To obtain the State Margin, the Brown Bear divides the previous sum by the sum of the weights. For Iowa in our example the State Margin is -35.58 ÷ 2,683.62 = -1.33%. Based on these results, the Brown Bear would designate Iowa Tossup (B) (since George Bush's margin is less than 2% points).

This is how the Brown Bear calculates the leader of the presidential race in each of the fifty states.