extrapolation of statistical tables
[critical]=extraptab(tab,n)
* tab = a (p x q) table where:
. the first row is not used (it is supposed to be filled with the size levels)
. each row has the form [n v1 ... vn] where n is a # of observations (filled from the lowest to the highest in col 1, starting from row 2, since row 1 is not used)
* n = a scalar (the # of observations for which critical are calculated by extrapolation)
* critical = a (1 x q) vector of critical values for all sizes present in the table tab