2008 General Election SOV Data by 2012 RG Precinct File Descriptions

Converting Previous Election Results to Current Geography Through Matching

Elections results can be associated with current geography in
different ways. A general discussion of how the Statewide Database
handles geographical assignment of election results is given in
``Creating California's Official Redistricting Database''
(available on the Statewide Database web site), and it is assumed that
the reader of this documentation is familar with the techniques
described in that document. The method described here uses the
technologies and techniques described in the ``Creating'' document,
and extends them to allow a rapid and relatively accurate conversion
of previous election results to any current geography.

As described in the ``Creating'' document above, each individual
voter is given a behavioral propensity of voting for a particular
candidate or proposition. These propensities were then used in the
creation of the unified dataset that was released in April of 2011.
While calculation of these propensities and the subsequent merger to a
common format are a time-consuming process, once calculated, these
propensities can be used to provide conversion of the election results
for which they were calculated to current electoral geography. This
is done in two complementary ways. First, the current registered
voters are matched to the registered voters from the previous election
those voters behavioral propsensities are associated with the
registration precinct of the current registered voter. Second, for
those registered voters that cannot be matched across the two
registered voter lists, a geographic conversion is created using the
matched registered voters, and election results that have not been
assigned are distributed through these conversions.

An example is given for Alpine County, allocating g10 election
results to the p12 registration precinct geography for Proposition 19.
Below, rgprec refers to the p12 registration precinct and srprec
refers to the g10 sr precinct (see the "Creating" document for a
description of these precincts and a description of how the
propensities are derived).

Number of registered voters g10: 781
Number of registered voters p12: 818
Number of voters who voted in g10: 553
Number of voters who voted in g10 matched to p12 registration: 486

Voting propensities are of the form (this is for g10 sr precinct 1)

PR_19_N PR_19_Y

left 0.275958 0.72355
right 0.618946 0.37944
ind 0.152179 0.84782

where the groups are an assignment of voters on the basis of
declared partisan affiliation (see the ``Creating''
documentation).

A voter who voted in the g10 election and who match a registered
voter in the p12 election are now used to calulate "matched"
voting results by p12 rg precinct, by summing the propensities
of these voters:

rgprec PR_19_N PR_19_Y
11 43.69 65.12
21 46.63 62.72
31 17.49 27.05
41 38.44 67.81
51 46.38 65.86
Totals 192.63 288.55

Now, to assign voting results for voters in sr precincts in g10
who are not matched to p12 voters, a conversion file is created
between the p12 rg precincts and the g10 sr precincts (using all
registered voters who match between the two elections, not just
those who voted). This conversion can be displayed as follows:

rg prec tot reg tot reg sr prec tot reg sr prec tot reg
matched 1 matched 2 matched
----------------------------------------------------------------
11 139 109 1 114 2 7
21 142 111 2 100 5 23
31 107 45 3 82 5 10
41 260 108 4 142
51 170 113 2 1 5 145

To allocate g10 results, "reverse" this mapping (that is, go
from g10 sr precinct to p12 rg precinct).

sr prec rg prec tot reg rg prec tot reg rg prec tot reg
1 matched 2 matched 3 matched
----------------------------------------------------------------
1 11 114
2 11 7 21 100 51 1
3 31 82
4 41 142
5 21 23 31 10 51 145

This then allows proportional allocation of sr precinct voting
results to p12 rg precincts.

Since the voters in the g10 srprecs who are not matched to the
p12 rg voters are known, they can be displayed by group.

1 ind 4 left 6 right 7
2 ind 4 left 8 right 9
3 ind 1 left 2 right 1
4 ind 5 left 5 right 6
5 ind 1 left 6 right 2

The above propensities can then be applied to obtain vote totals
by srprec.

srprec PR_19_N PR_19_Y
1 6.60 10.39
2 9.61 11.07
3 1.35 2.60
4 5.61 10.17
5 2.97 5.94
Totals 26.14 40.17

The voting totals by srprec are also known:

srprec PR_19_N PR_19_Y
1 47 74
2 54 65
3 16 25
4 45 80
5 62 91
Totals 224 335

Also known are the "matched" totals by g10 sr precinct (note the
county totals match those for the p12 rg precincts given above,
though the individual table entries won't generally agree as
precinct boundaries shift between elections and sr precincts and
rg precincts are often not directly comparable).

srprec PR_19_N PR_19_Y
1 39.98 61.93
2 43.50 52.86
3 12.93 23.65
4 38.44 67.81
5 57.78 82.31
Totals 192.63 288.55

Adjustments are then made to the propensities to obtain equality
of the voting results to the sum of the matched and unmatched
voting results.

Finally, the adjusted unmatched totals are mapped back to the
p12 rg precincts and, together with the matched totals, give a
description of the g10 voting results by p12 rg precinct.

Matched Unmatched SOV Totals

rgprec PR_19_N PR_19_Y PR_19_N PR_19_Y PR_19_N PR_19_Y
11 43.69 65.12 7.70 12.86
21 46.63 62.72 10.27 12.37
31 17.49 27.05 3.31 1.84
41 38.44 67.81 6.56 12.19
51 46.38 65.86 3.54 7.20
Totals 192.63 288.55 31.37 46.45 224 335

The SOV totals for p12 rg precincts cannot be known but only
estimated, but the estimated totals do sum to the county totals.

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