On 1 Mar 2004 13:27:17 -0800, Euh <[EMAIL PROTECTED]> wrote: > I took 3 differents samples from the flask and, for each sample, I did 20 > counts under the microscope (= at 20 different
I've considered all counts from any samples as equal cases. Maybe we need consider only means of counts as cases, and then calculate a mean of the cases (samples). The formula for required number of cases is n = (t^2*s^2)/(d^2) n - number of cases t - Student factor s^2 - dispersion d - maximum allowable error You need to define these parametrs: 1) confidence probability of 0.95 is quite enough for biological investigations; so, choose p=0.95; t(0,95)=1,96; 2) maximum error; assume +-10 particles; 3) calculate dispersion using your data (according the data you gave bellow your posting s=34 for all 60 cases). So, n=(3,84*1156)/100=44 I offer to calculate 45 counts per sample; and use 5-10 samples . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
