HALL A C++/ROOT Parity Analyzer  Pan

       TaStatistics.cc  (implementation)

 Author:  R. Holmes <http://mep1.phy.syr.edu/~rsholmes>, A. Vacheret <http://www.jlab.org/~vacheret>, R. Michaels <http://www.jlab.org/~rom>, K.Paschke
 @(#)pan/src:$Name:  $:$Id: TaStatistics.cc,v 1.9 2003/07/31 16:12:00 rsholmes Exp $



    A general purpose statistics class, allowing accumulation of
    sums for one value or a set of values, from which quantities
    such as means, widths, errors, etc. can be computed.

    Note that this class permits a single-pass analysis with *no*
    attempt to reduce errors on the computed quantities.  Such an
    analysis, using mathematically correct formulas, can still give
    badly erroneous results for RMS / variance / error due to
    roundoff problems.  In particular, when N is large and the
    variance is small, mean(x^2)-(mean(x))^2 is a difference of two
    large numbers and can have very poor precision.  Results can be
    improved by making an estimate of mean(x) and subtracting this
    from each x_i, but automating such an estimate is difficult.

    However, this class also allows 2-pass calculations to be made
    if desired, with greatly improved precision.  Note that in
    practice the aforementioned roundoff problems have not been
    shown to be significant for HAPPEX data.  For more on this
    subject see for example _The American Statistician_ V. 37 p. 242
    (1982).