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DRAFT COUNTY PROFILE (DATA) ELEMENT APPENDIX
<br />Adjusted Migration Model: Explanation Of Methodology
<br />As prepared by the NC Office of Budget, Planning and Management, Demographic Section
<br />Population Projections Desgdption
<br />The North Carolina Office of State Budget and Management in June of 2006 released the current
<br />set of population projections for the state and its counties. The greatest difference between these
<br />projections and the previous ones (released in 2005) is the difference in assumed growth trends
<br />for the three decades from 2000 to 2030.
<br />The basic assumption is almost the same for both series. For the previous set of projections, the
<br />assumption was that migration (and, hence, growth) for July 1, 2004 through April 1, 2030 was a
<br />function of two sets of growth. The first set was the "trend" growth based on the 1990-2000 base
<br />decade, The.second was the average annual growth from April 1, 2000 through July 1, 2004
<br />derived from the set of July 2004 Provisional County Estimates which was released by the State
<br />Demographer in April of 2005. For the current set of projections, the assumption is that
<br />migration (and, hence, growth) for July 1, 2005 through April 1, 2030 is also a function of two
<br />sets of growth. The first set is the "trend" growth based on the 1990-2000 base decade, The
<br />second is the average annual non-institutional growth from April 1, 2000 through July 1, 2005
<br />derived from the set of July 2005 Provisional County Estimates which was released by the State
<br />Demographer in May of 2006.
<br />The basic growth functions were slightly different. For both sets of projections, the first two
<br />years after the estimate date, 2004-2006 for the previous set of estimates, 2005-2007 for the
<br />current set of estimates, were considered "transition" years between the proVisional estimates and
<br />the long range projections. For subsequent years, until April 1, 2010, the growth was assumed to
<br />approximate a weighted average of the "trend" growth and the "estimate" growth. For the
<br />previous set of projections, the "trend" growth was weighted at 60% (and, hence, the "estimate"
<br />growth was weighted at 40%). For the current set of projections, the "trend" growth was
<br />weighted at 50% (and, hence, the "estimate" growth was also weighted at 50%). The county
<br />totals for April 1, 2020 were adjusted for both sets of projections to try to maintain migration for
<br />April 2010 to April 2020 at close to the same levels as those of the last years of the 2000s.
<br />The "transition" years were treated somewhat differently. For the previous set of estimates, the
<br />same "estimate" growth was used during the "transition" years as was used for-the following
<br />years. For 2004-05, the "estimate" growth was weighted, however, at 80%, and, for 2005-06, at
<br />60%, instead of at the normal 40%. For the current set of projections, the "estimate"
<br />growth was always weighted at 50%, but the growth used was different for the transition years..
<br />For 2005706, the "estimate" growth was that of July 1, 2004 to July 1, 2005. For 2006-07, the
<br />"estimate" was the one half of the July 1, 2003 to July 1, 2005 growth.
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<br />8/16/2007
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