First, remember that only ZCTAs reporting 11 or more patients from a health center are counted. The most likely explanation of this scenario is as follows: two years ago, that ZCTA had fewer than 11 patients reported by the health center. In the following year, the same ZCTA had 11 or more patients reported. Finally, the next year, the ZCTA reported fewer than 11 patients. For example, the ZCTA may have had 8 patients reported in 2019, 11 in 2020, and 9 in 2021. When the 2-year % change in patients is calculated, only 2019 and 2021 data are examined. Since there were less than 11 patients, zero patients were reported in those two years so the % change layer is displayed as blank. However, when the one year % change in patients is calculated, 2020 and 2021 data are examined. This showed that the number of patients decreased from 11 in 2020 to 0 in 2021. This accounts for a 100% loss in patients and colors the ZCTA red. Be careful in interpreting these % change layers when the number of patients is small.
