The district partisan index is a unique calculation used to project the underlying partisanship of a given district in a specific general election. Because of turnout differences, an index score for a specific Assembly district would be different in a presidential year versus a non-presidential year.
Used in the calculation are results from previous elections and voter registration, weighted for the given election. Strong underlying partisanship for one party does not mean that party will win the seat, as candidates, candidate performance, and significant trends must be considered, which are used for District Lean.
While the ATC partisan index seeks an objective measurement of the underlying partisanship of a given district, District Lean is a subjective projection of the likelihood a party will capture the seat in the general election. This rating considers both the underlying ATC Score as well as candidates, candidate quality, fundraising, independent expenditures and trends.