Application of bootstrap method for evaluation of the average concentration of Radium-226 in forage palm (Opuntia spp)

The distribution of natural radionuclides in samples from typically anomalous environments has generally a great significant asymmetry, as a result of outlier. For diminishing statistic fluctuation researchers, in radioecology, commonly use geometric mean or median, once the average has no stability under the effect of outliers. As the median is not affected by anomalous values, this parameter of central tendency is the most frequently employed for evaluation of a set of data containing discrepant values. On the other hand, Efron presented a non-parametric method the so-called bootstrap that can be used to decrease the dispersion around the central-tendency value. Generally, in radioecology, statistics procedures are used in order to reduce the effect results of the presence of anomalous values as regards averages. In this context, the present study had as an objective to evaluate the application of the non-parametric bootstrap method (BM) for determining the average concentration of 226Ra in cultivated forage palms (Opuntia spp.) in soils with uranium anomaly on the dairy milk farms, localized in the cities of Pedra and Venturosa, Pernambuco-Brazil, as well as discussing the utilization of this method in radioecology. The results of 226Ra in samples of forage palm varied from 1,300 to 25,000 mBq.kg-1 (dry matter), with arithmetic average of 5,965.86 +- 5,903.05 mBq.kg-1. The result obtained for this average using BM was 5,963.82 +- 1,202.96 mBq.kg-1 (dry matter). The use of BM allowed an automatic filtration of experimental data, without the elimination of outliers, leading to the reduction of dispersion around the average. As a result, the BM permitted reaching a stable arithmetic average of the effects of the outliers. (author)