Retirement slump refers to the average falloff in the party's vote when the incumbent retires. A positive value of the sophomore surge represents an incumbency advantage. The retirement slump should be positive for an incumbency advantage to exist.

Sophomore surge A sophomore surge (sometimes referred to in the United Kingdom as first-term incumbency bonus) is a term used in the political science of the United States Congress that refers to an increase in votes that congressional candidates (candidates for t ...

is the average vote gain for freshman winners in election 1 who run again in election 2. Retirement slump is the average vote loss for the parties whose candidates won election 1 and did not run in election 2.http://gking.harvard.edu/files/inc.pdf When a

and a Retirement slump combine, it is what is called a slurge.

References

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