Sampling bias and sampling errors in pollen counting in aerobiological monitoring in Italy.

Information about airborne pollen concentration is of concern for health authorities across Europe. The reliability of data estimates depends on the accuracy and precision of pollen counts. In Italy, pollen counts are carried out on slides for microscopic evaluation and are regulated by the national Standard UNI 11108:2004. Our results showed that counts performed according to the Italian standard may result in a significant bias in the number of pollen grains counted and this will have an impact on final estimates of pollen concentration. For the same sample size, confidence intervals vary in relation to pollen abundance, either in terms of number of grains or of number of species. The sample size suggested by the standard (20% of the target surface) may result in errors in pollen counts ranging from 7-55% of the mean value, and in missing 22-54% of the taxa present on the slide.