If I can jump into this one without going off the deep end...... If you are measuring something, such as concentration of trace element in a solution, there are occasions when the reported concentration is "0" - nada, zero. In fact, the reported value should be "not detected", or "less than x," where x is the minimum detectable amount.
If you are trying to evaluate results in which this type of number is part of the discussion, I suggest you put in the minimum detectable amount, or perhaps a bit less. See what happens then. Jay Garbriel wrote: > I have a question. Thanks a lot for your help, > It is about statistics in computing phi correlation coefficient: ( which > is a special formula for the Pearson product-moment correlation in the > particular case of two binary variable.) > > We used the method described in > > http://www.cmh.edu/stats/definitions/phi.htm > > See the following contigency table , > > Y+ Y- > ------------- > X+ |a11 | a12| > ------------ > X- |a21 | a22| > ----------- > > Defination of Phi, > > a11*a22 - a21*a12 > phi= --------------------------------------------- > sqrt((a11+a12)*(a21+a22)*(a11+a21)*(a12+a22)) > > phi>0.7 strong correlation. > phi>0.3 weak correlation > > However, there is limitations in this calculation, > > since if X- is zero, so, a21=0, a22=0; > ************************************* > There will appear 0/0. > (and also big problem in p_value calculation). > > How to solve this? Is there any other method to quatitfy this when > denominator (4 sums) appear 0? ( I think phi correlation coeeficient is > not qualified to this situation.) And also compute p value or other > statistics term in this situation? > . > . > ================================================================= > Instructions for joining and leaving this list, remarks about the > problem of INAPPROPRIATE MESSAGES, and archives are available at: > . http://jse.stat.ncsu.edu/ . > ================================================================= -- Jay Warner Principal Scientist Warner Consulting, Inc. 4444 North Green Bay Road Racine, WI 53404-1216 USA Ph: (262) 634-9100 FAX: (262) 681-1133 email: [EMAIL PROTECTED] web: http://www.a2q.com The A2Q Method (tm) -- What do you want to improve today? . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
