The NAB pollen and mold spore levels were developed using the chart below. The concentrations in the chart (pollen or spores per cubic meter) were statistics from all certified counting sites. The levels correspond to different ranges for each of the pollen categories and for fungal spores. The concentrations were translated into levels based on the following:
• Low levels are concentrations that are less than the median or 50th percentile (i.e. half the counts were below the median.)
• Moderate levels are concentrations that fall between the 50th and 75th percentile
• High levels fall between the 75th and 99th percentile
• Very high levels are above the 99th percentile (99% of the counts are below this level)
Based on these definitions, we suggest the following ranges for low, moderate, high, and very high.
These levels and the corresponding ranges are based entirely on ecological measurements, not on health effects. Because the data were from all certified counting stations, the ranges allow comparisons between sites across the country and may be more appropriate than a range based on local numbers. This does mean that, for some stations, some categories will never be high. Because of this, a few stations have determined the ranges for their own locations and do not use these national ranges.