sample pool - (Dec/15/2010 )
hi 
when we pool samples how do we calculate standard deviation and variance?
thank you
"pool samples"...do you mean combine sample volumes into one container? Or obtain samples and have them as a single population?
combine sample volume taken from subjects of same study group. suppose we have 8 subjects in one group then combining the sample obtained from each subject to form one sample.
sgt4boston on Thu Dec 16 11:23:27 2010 said:
"pool samples"...do you mean combine sample volumes into one container? Or obtain samples and have them as a single population?
Never came across this approach. Usually collect samples from control and experimental groups and compare them (compare the group as a whole or break down into subsets).
If pooling samples from experimental then you would need to do same with control.
Individual samples should be taken from two groups then analytically compared.
yes ofcourse we have to treat test and control groups in same way....what if we need 50 microL of sample for a particular sample but we are getting 10 microL from each subject... in this case we pool samples. if we have 8 subjects in a group (test as well as control) we will be having 80 microL sample..than we can use 50 microL sample to perform experiment.The value which we get as a result of the experiment is considered as mean value...so we have two mean values one from test and one from control.So, now the problem is the comparision...we wont have standard deviation (SD) to calculate significance of result...so my problem is that how can we compare two means widout SD?
sgt4boston on Thu Dec 16 21:02:19 2010 said:
Never came across this approach. Usually collect samples from control and experimental groups and compare them (compare the group as a whole or break down into subsets).
If pooling samples from experimental then you would need to do same with control.
Individual samples should be taken from two groups then analytically compared.
Essentially you can't - you need to get more samples(groups) which you can compare to your control.
For most experiments not the volume but the concentration of amount of substance matters.
I don't know whether your experiments are exceptions, but if not, then why don't you just fill up your 10 µl sample to 50 µl?
I agree with bob1, you neither have a mean nor standard deviation: if you pool your samples to one sample and then measure, you have just one data point.
Chakchel's idea would be a solution (if it's possible), then you have several measurements and can calculate mean + SD.
it depends upon the sensitivity of method...10µl will have less amount of analyte than 50µl.
for exmaple: if 10µl sample contain 2mg protein then 50µl will contain 10mg.
Chakchel on Fri Dec 17 09:40:18 2010 said:
For most experiments not the volume but the concentration of amount of substance matters.
I don't know whether your experiments are exceptions, but if not, then why don't you just fill up your 10 µl sample to 50 µl?
sorry...2 means to compare but no SD...
hobglobin on Fri Dec 17 10:14:17 2010 said:
I agree with bob1, you neither have a mean nor standard deviation: if you pool your samples to one sample and then measure, you have just one data point.
Chakchel's idea would be a solution (if it's possible), then you have several measurements and can calculate mean + SD.