Electoral Math
Reality-Based^TM Political Numbers from Nicholas Beaudrot

Election 2006: The Good, The Bad, and The Ugly | Home | Partisan Realignment Maps: Tennessee

Partisan Realignment Maps: Pennsylvania

Update: I've changed the scale of the map slightly; now, counties whos net Democratic performance stayed with 0.5% of the 2004 results show up as white.

This week, I'm going to roll out a series of maps demonstrating the change in partisan alignment in competitive Senate races between 2004 and 2006. While almost every county became more Democratic, these maps show which became more Democratic than the state as a whole. The calculation used is:

(SenateDem06_County – SenateDem06_State) –  
    (PrezDem04_County – PrezDem04_State)

So, for example, let's take Erie County, Pennsylvania; the darker pink county in the Northwest corner of the state.

• In 2004, John Kerry got 53.1% of the two-party vote in Erie county, while winning all of Pennsylvania with 51.2%. So in '04, the county was 53.1 – 51.2 = 2.9% Democratic.
• In 2006, Bob Casey, Jr. won Erie County with 59.6%, while earning 58.7% of the vote across all of Pennsylvania, making the county 59.6 – 58.7 = 0.9%
• So, over two years, the county's partisan index shifted by 0.9 – 2.9 = -2.0%, meaning that the county appears to be grown Democratic more slowly than the rest of the state since 2004. [Updated to provide clearer language]

Obviously, it's easy to read too much into these numbers. For instance, the largest shift towards Republicans in Pennsylvania occured in Philadelphia County (and city). Philly moved from 81-19 Kerry to 84-16 Casey while the state as a whole swung towards casey by 9%. Does this mean that the city became "more Republican"? Of course not; it's more likely that there are so few urban Republicans left that there isn't much room for improvement. In fact, most of "more Republican" counties are already heavily Democratic areas in Pittsburgh, the Philly suburbs, and the Northwest (the few counties in the Northeast are exceptions; all went for Santorum by modest margins).

Still, we can spot a clear trend in the Pennsylvania map. Central Pennsyvlania shows the strongest shift towards Democrats; more so than the rural regions in either the West or the East of the State. This bodes well for the long-term realignment of Pennylvania; if Democrats can maintain their strength in central Pennsylvania, they'll be able to move the state into the Democratic base, which means winning the Presidency gets much easier

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Last updated by Nicholas Beaudrot on 09:02 14 November 2006