Housing Market Index. The HMI is based on a monthly survey of home builders that the National Association of Home Builders (NAHB) has been conducting for over 16 years. Each month, the survey asks builders to rate present sales of single-family detached homes and sales expectations over the next six months as "good," "fair," or "poor." Traffic of prospective buyers is rated as "high to very high," "average," or "low to very low." The HMI is a weighted average of the three seasonally adjusted components. On a scale of 0 to 100, with zero being the worst and 100 the best.