(a) Your service and the traveling habits of your customers change naturally over time.
(b) To meet certification requirements:
(1) Such service and habit changes may increase the statistical variation in key quantities (e.g., PMT, APTL) and hence require larger sample sizes.
(2) The sampling plans produced by this template are only certified to meet FTA’s requirements of 95% confidence with 10% precision for certain sampling cycles, presuming no major changes in your service.
(3) After this time, or after major changes in your service, a new template sampling plan must be developed to maintain certification of compliance with the FTA requirements.
(c) To get more efficient sampling plans:
(1) Such service and habit changes sometimes may reduce the statistical variation of key quantities (e.g., PMT, APTL).
(2) You would be able to take advantage of such reduced variation by revising your template sampling plans using your most recent sample data that reflect these service and habit changes.