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NHST : Accuracy and Precision
Posted:
Oct 14, 2013 4:49 PM


NHST : Accuracy and Precision
http://en.wikipedia.org/wiki/Accuracy_and_precision
In classical Null Hypotheses Statistical Tests the ONLY result/conclusion we can attain, given data and confidence level: ___we obtain sufficient evidence the null is unlike ___we does not.
Any other one more *specific* sometimes found in textbooks /papers is unlawful/absurd/wrong.
The difference of two means
The true difference between Population means. D= muX muY is accurate (ACCURACY) relative to the observed difference, D´= xbarybar, if  D  D´  is short. By the other hand high PRECISION demands that the Confidence Interval CI = [u, v] containing D´ with a probability alpha ( = 0.95, so) be short.
_______________________u________v__ ________________________________________ __________ D_______________D´______
ACCURACY and PRECISION have rather different features and controlling ways: ____ACCURACY: we can establish the probability to find D inside the confidence interval, u<= D <=v, say 95% Confidence Level. In contrast PRECISION  how wide or narrow is the interval  is left to the Goods of Chance to decide: we are unable a priori to preview because are dispersion data immediately dependent. It can happens even that a high precise value be be useless/trash because the CI does not contain D . . . a present type I error (fee figure above).
Luis A. Afonso



