[snip] > Thank you David. It's liquid, not gel. > I am trying to readress the question as follows: > > The question is now "how to distinquish a bag that is 1000 bacterial > per ml from a bag that is 10 bacteria per ml? How many samples of 1 ml > should be taken out of a 60 ml bag? (0.9 power and 0.05 level of > significance) > Any way to estimate the variance? > > Aron
It's seems like this newly phrased "question" is much easier to answer than the orginal one posted. I don't know any specifics about this topic (bags of liquid with bacteria) but if I extract one ml out of a bag of "1000 bacterial per ml" liquid, wouldn't I get something pretty close to 1000 bacterial? (Give or take some, sure, but somewhere around there). Then if I make a 1 ml extraction from the 60 bacterial per ml bag, I'm going to get something around 60. Maybe more, maybe less, but nowhere near 1000. So I would expect I could take two or three samples (if not just one) of 1 ml from each bag and be pretty darn certain which bag is the 1000 per and which is the 60 per. Now... if the question was "Tell the difference between a 1000 per/ml bag and a 900 per/ml bag" then I would be a bit more concerned about what the variance is. As usual, my question is, "Does this make sense?" -Brian Brian Teasley www.teasley.net . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
