The percentage change in home values (represented by each bar in the chart) is simply the price change relative to the same quarter one year earlier. For example, if the HPI release is for the second quarter, then the price change reports the percentage change in values relative to the second quarter of the prior year. It reflects the best estimate for how much the value of a typical property increased or decreased over the four-quarter period.
A word of caution: do not add up consecutive numbers to determine how much a home price has changed from an earlier time. The values represented by each bar already represent the change from the same quarter of the previous year. Values above the line represent a time period where there was appreciation in the market. Values below the line indicated periods where home prices have depreciated from one year ago. The trends in the chart (the upward and downward movement) show whether we are heading in a positive direction or negative.