Yahoo! Finance reports the index that measures sales agreements for previously occupied homes fell 11.6 percent in April to 81.9, according to the National Association of Realtors (NAR).  A count of 100 is considered healthy.  The last time the index hit 100 was April 2010, the last month when people could take advantage of the $8,000 tax credit.  Signed contracts are indicative of the future of the market because of the one-to-two-month delay between the signing and the closing of the deal.  Last year the sales of previously occupied homes fell to their lowest level in 13 years.  Even though there are 120 million more people in the U.S. now than in 1963, the number of purchases of previously occupied homes is half the rate of 48 years ago.