Hi Reza, can you just specify how many subjects, how many tests? Thanks

Can you please tell more about the design of your study? And what do you mean with a sample size of 3*4?

We need more information about your study.

thanks for reply.

please take  a look at the following example:

we have  fixed concentrations of a variable( categorical). let's say, 0, 10 and 20 ug. and we have four different concentration of each variable, let's say, 0, 10,20 and 40 ug. in the latter, each group has a concentration(continuous). please take a look at the attachment file.

so now, I am wondering to know whether there is any significant combination between each different concentration (I mean drug interaction or combination).

please note that these measuring were repeated in three different days.

I want to know if each concentration  is significant per se or when they are combined.

Thanks,

Depends on your methods and type and manner of data collected.  Your best bet is to always consult with a statistician in your study design and also after your data is collected.