An index that measures the confidence of home builders was unchanged in May, suggesting virtually no improvement in the moribund U.S. housing market, MarketWatch reported. The National Association of Home Builders said its Housing Market Index (HMI), produced in tandem with Wells Fargo & Co., remained “at the low level of 16.” Economists surveyed by MarketWatch had expected the HMI to rise to 17. The HMI is a seasonally adjusted index in which any number over 50 indicates that more builders view sales conditions as good rather than poor. The last time the index topped 50 was in April 2006.