A builder’s business depends on being able to gauge how interested Americans are in buying a house. After all, no one would go through the labor and expense of building a house without feeling confident that they’d be able to find a buyer once it was finished. That’s why the National Association of Home Builders measures builder confidence each month. If builders are optimistic and building homes, there’s a good chance the overall housing market is also doing well. In December, the NAHB’s Housing Market Index – which is scored on a scale where any number above 50 indicates that more builders view conditions as good than poor – reached 76. That’s the highest reading since June 1999. Greg Ugalde, NAHB’s chairman, said builders are responding to a rebound that began last spring. “Builders are continuing to see the housing rebound that began in the spring, supported by a low supply of existing homes, low mortgage rates, and a strong labor market,” Ugalde said. Among index components, the one measuring current traffic saw the biggest month-over-month improvement, rising seven points to 84.