persistency

Percentage of life insurance or other insurance policies remaining in force; percentage of policies that have not lapsed. The higher the percentage, the greater the persistency. Since it is an important measure of a company's retention of its life insurance business, most companies extend every effort to increase persistency. See also Conservation.

noun

1. The state or quality of being insistent: insistence, insistency, perseverance, persistence. See continue/stop/pause.
2. Uninterrupted existence or succession: continuance, continuation, continuity, continuum, duration, endurance, persistence. See continue/stop/pause.

(DOD, NATO) In biological or chemical warfare, the characteristic of an agent which pertains to the duration of its effectiveness under determined conditions after its dispersal.

The noun has one meaning:

Meaning #1: persistent determination
  Synonyms: doggedness, perseverance, persistence, tenacity, tenaciousness, pertinacity