Analysis of the Ambrosia pollen data from our lab found highly significant correlations (r > 0.95, p < 0.001) between concentrations determined by different counting methods, and the methods were considered roughly synonymous in estimates of the daily concentrations ( 47 ).
Linear regression of the APIn over time showed a trend to lower concentrations but no significant change; however, there was a significant decrease (R 2 = 0.139, p = 0.033) in the peak concentration during the 33 years ( Table 4 , Figure 5 ).
The peak concentration also had an increasing trend ( Table 4 ) but it was not significant at the 5% level.