a question of sufficient n's

John Hines hines at pharm.med.upenn.edu
Thu Aug 12 17:13:35 EST 1999


A friend posed a question to me last night.  I have my own opinion and I
gave it to him.  I would be interested in hearing what other scientists
might think on the matter:

I will change the details a little just to protect the innocent.

The experiment being conducted measure the effect of a particular drug on
the levels of certain liver enzymes.  The levels of the enzymes will be
quantitated by western blotting.

In the experiment, 8 mice are treated with the drug for the prescribed
time and dosage and 8 mice are treated with vehicle.  Their livers are
pooled according to treatment group (drug or control) and homogenized. 
SDS-PAGE is done and the
blots are performed.

Now, if the scientist runs a 7 lane gel, where:

lane 1 = MW markers

lane 2, 4, 6 = control homogenate

lane 3, 5, 7 = drug treated homogenate

and then blots the entire piece of nitrocellulose for the level of target
enzyme, is that 3 replicate measurements (comparing lane 2 vs. 3; 4 vs. 5;
6 vs. 7) ??   Or is that an n of 3?





or second scenario:

if the scientist runs a 3 lane gel, where:

lane 1 = MW markers

lane 2 = control homogenate

lane 3 = drug treated homogenate

and blots for the enzyme.  And then runs a second identical gel next week and 
blots that; and then runs a third identical gel the following week and
blots that; is that 3 replicate measurements (remember, the very same
homogenates
were used in all the blots), or is that an n of 3??



The answer to me seems pretty obvious in either scenario, but I'd like to 
hear other opinions too.

John

hines at pharm.med.upenn.edu



More information about the Proteins mailing list