back to County Voting Patterns in US Presidential Elections, 1976-2000

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A grid series analysis was performed to determine and show how many times each county switched its vote plurality from one party to another. It was unnecessary to add further data to the shapefile tables for this analysis. Rather, we used the grids created for the first analysis (voting history) to make a comparison between grid cells for each pair of elections (1976 to 1980; 1980 to 1984; 1984 to 1988; 1988 to 1992; 1992 to 1996; and 1996 to 2000).

We used Map Calculator to perform the function "aGrid.Combine (aGridList)" to take data fields from each of the two grids being compared and place them together in a new grid. The function's format is [gridA].combine({[gridB], [gridC], ... [gridN]}). For example,

([G1976].combine({[G1980]})). The result was a file with four fields:


where Gyyyy was the PartyValue field from the grid (Republican=-1, Democrat=1).

The two PartyValue fields could have 9 possible value pairs, which represent several conditions (see Table 5 for the possible pairs).

Table 5
Gyyyy Gyyyy(+4) Possible results
1 1 Democrat both elections
1 0 Democrat to Tie or No Data
1 -1 Democrat to Republican
0 1 Tie or No Data to Democrat
0 0 Tie or No Data to Tie or No Data
0 -1 Tie or No Data to Republican
-1 1 Republican to Democrat
-1 0 Republican to Tie or No Data
-1 -1 Republican both elections

Of these nine possibilities we were most interested in the instances where a county definitively switched from one major party to another. The pairs with zeros were quite rare (and we also didn't know if they were Ties or No Data) so we lumped all pairs with a zero together into one class. That left us with 5 possible classes, which we numbered in order to apply a legend file. A new field was created called ŒswitchCode' and labeled 1 to 5 (see Table 6).
Table 6
switchCode Gyyyy Gyyy(y+4) Label
1 1 1 Dem
2 1 -1 Dem to Rep
3 -1 -1 Rep
4 -1 1 Rep to Dem
5 One or two zeroes No Data

To each of the six election pair tables we added a new field called ŒswitchedParty'. Value pairs 2 and 4 were coded Œ1,' while pairs 1, 3 and 5 were coded 0. Click here to see the seven individual maps. (Scroll down for main map.)

When all six grids were created and coded, Map Calculator was used to add together [( [1976_1980 . switchedParty] + [1980_1984 . switchedParty] + [1984_1988 . switchedParty] + [1988_1992 . switchedParty] + [1996_2000 . switchedParty]) + [1992_1996 . switchedParty]] the ŒswitchedParty' fields to yield a new grid showing the number of times each area of the grid changed party allegiance over the past 7 elections (see Figure 7).
The possible values ranged from 0 (voted for the same party in every election from 1976 to 2000) to 6 (voted for a different party in every election from 1976 to 2000).