Builder confidence in the market for new single-family homes edged up to 21 in December from 19 the previous month, the National Association of Home Builders said today. This is the third month in a row that builder confidence has improved, the organization said. The index gauges builder perceptions of current single-family home sales and sales expectations for the next six months as “good,” “fair” or “poor.” The survey also asks builders to rate traffic of prospective buyers as “high to very high,” “average” or “low to very low.” Scores from each component are then used to calculate a seasonally adjusted index where any number over 50 indicates that more builders view conditions as good than as poor.