Workers insured under the Social Security program are categorized as fully and permanently insured, fully but not permanently insured, or insured in the event of disability. The number of workers (in millions) in each insured category from 2000 to 2015 are provided in the accompanying table.

a. Compute a simple composite index for the number of workers in the three insured categories using 2000 as the base period.
b. Is the index, part a, a price index or a quantity index?
c. Refer to part a. Interpret the index value for 2015.

Fully, permanent Fully, not permanent Event of Year disability 2000 2001 2002 2003 140.9 142.9 144.9 147.0 44.9 45.2 45.3 45.0 139.5 141.7 143.5 144.9 149.0 151.1 153.3 155.4 157.4 2004 2005 2006 2007 2008 44.8 44.7 45.1 45.6 46.0 146.2 147.7 150.1 152.3 154.5 2009 2010 2011 2012 2013 2014 159.2 161.1 163.1 163.3 165.3 167.3 44.8 44.6 44.3 44.0 43.9 43.8 150.6 151.7 152.6 149.2 149.9 150.6 2015 169.4 43.8 151.2