bootstrap u test p values small counts aberrations

[jorgeegm]

Technical details

• Version:3.5
• Assessment: u test
• Module: Fitting and Dose estimation

Issue description

u test deviations from normal distribution is quite evident for yields <0.1 see Merkle 1981, and Higueras et al. 2018.
If u test prevail over exact conditional tests
still care should be taken for small aberration counts or small yield in these cases bootstraping the statistic under H0 could be a proper solution.
Eg. Note similar solutions implemented for Chisquare test in R stats when simulated p values are provided for small frequencies. An alternative to the use of a conditional exact test with lack of statistical power and as alternatuve to deviations from the chi square distribution under H0 if chisquare aproximation is used.

This a solution usefull if comparison of poisson means or counts are introduced in biodosetools avoid t aproximations and use exact poisson test eg. exactci R package. To detect and exposure higher than background of aberrations (dicentrics)