Posts tagged ‘Oregon House ’02-’08 Analysis’

Partisanship Became an Increasingly Strong Factor in House Contests from 2002 to 2008

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This post will look at the model from the last post in more detail.

The error rate of predicting House District contests declined from 2002 through 2008. This implies that partisanship made more and more of a difference to voters over time.

As partisanship became more important, Republicans held fewer and fewer House seats.

The analysis was performed using a logistic regression of partisan registration difference as the independent variable and winner of the contest as the dependent variable for all Oregon House District contests from 2002 through 2008.

Source of data: Oregon Secretary of State.

Partisan Registration as a Predictor of Oregon House District Result, 2002 through 2008

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The partisan registration difference alone can accurately predict 91% of the House contests from 2002 through 2008.

On its surface, this is not that interesting. Put it another way, and it really stands out: campaign quality differences, campaign expenditures differences, and candidate incumbency factors, etc., among other facts, are only needed to explain 9% of the outcomes.

This model holds during the great Republican year of 2002 and the “bad” Republican years of 2006 and 2008.

The analysis was performed using a logistic regression of partisan registration difference as the independent variable and winner of the contest as the dependent variable for all Oregon House District contests from 2002 through 2008.

Source of data: Oregon Secretary of State.

Oregon House Districts: Comparing the 2002-2008 Registration Change with the 2002 Registration Difference

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In general, the Democratic districts became more Democratic and the Republican districts became more Republican. The partisan geographic split in Oregon has increased since 2002.

There is a positive correlation of 0.59 which is statistically significant (>99% confidence the correlation is significantly greater than zero).

2002 Registration Difference: Republican registration percentage minus Democratic registration percentage.

Registration Change 2002 to 2008: 2008 Registration Difference minus 2002 Registration Difference.

Source of data: Oregon Secretary of State

Switched House Districts since 2002 and Oregon 2008 House District Partisanship

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This graphic presents the middle 20 Oregon House Districts by partisan registration difference (Democratic percentage minus Republican percentage).

Red districts are held by Republicans in 2008. Blue districts were held by Democrats from 2002 through 2008. Green districts switched from Republican to Democrat after the 2002 election.

No district outside the current middle 20 switched sides during the period.

Source of data: Oregon Secretary of State

Oregon House District Partisan Registration Change 2002 to 2008: Willamette Valley

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The greatest movements towards Democrats in the Willamette Valley happened, generally, in the most Democratic areas: Corvallis, Eugene, and Portland.

The Portland suburbs and Salem experienced the next largest shifts towards Democrats.

This map shows the relative changes in net partisan registration by Oregon House District between 2002 and 2008.

The House District boundaries were redrawn in 2001 and have not changed since.

Source of data: Oregon Secretary of State.

Oregon House District Partisan Registration Change 2002 to 2008: Portland Metro

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The greatest shifts in House Districts towards Democrats happened in the most Democratic areas. The greatest shifst happened, generally, in central Portland. The magnitude of the shift declines as one moves further out. These shifts reinforced existing trends.

This map shows the relative changes in net partisan registration by Oregon House District between 2002 and 2008.

The House District boundaries were redrawn in 2001 and have not changed since.

Source of data: Oregon Secretary of State.

Oregon House District Partisan Registration Change 2002 to 2008: Statewide

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This map shows the relative changes in net partisan registration by Oregon House District between 2002 and 2008.

The districts with the strongest trends towards Democrats are generally in western Oregon, particularly in the Eugene and Portland areas. The eastern, more safely Republican areas, have also shifted the least towards the Democrats.

Source of data: Oregon Secretary of State.

Oregon House District Seat Changes 2002 to 2008: Willamette Valley

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This map shows how Oregon House District representation has changed between 2002 and 2008.

Most of the changes from Republican to Democrat have been in Salem or on the  Oregon Coast or on the outskirts of Eugene and Portland.

The House District boundaries were redrawn in 2001 and have not changed since.

Color coding of map:
Red: Republican from 2002 through 2008.
Blue: Democratic from 2002 through 2008.
Yellow: Changed from Republican to Democratic in 2004, 2006, or 2008.

Source of data: Oregon Secretary of State.

Oregon House District Seat Change 2002 to 2008: Portland Metro

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This map shows how Oregon House District representation has changed between 2002 and 2008.

Republicans have tended to lose districts in the suburbs of Portland.

The House District boundaries were redrawn in 2001 and have not changed since.

Color coding of map:
Red: Republican from 2002 through 2008.
Blue: Democratic from 2002 through 2008.
Yellow: Changed from Republican to Democratic in 2004, 2006, or 2008.

Source of data: Oregon Secretary of State.

Oregon House District Seat Changes 2002 to 2008: Statewide

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This map shows how Oregon House District representation has changed between 2002 and 2008.

Most of the districts that switched from Republican to Democratic are in northwestern Oregon, between Eugene and Portland and along the coast. No districts have changed from Democratic to Republican.

The House District boundaries were redrawn in 2001 and have not changed since.

Color coding of map:
Red: Republican from 2002 through 2008.
Blue: Democratic from 2002 through 2008.
Yellow: Changed from Republican to Democratic in 2004, 2006, or 2008.

Source of data: Oregon Secretary of State.