Why do we only study one independent variable at a time?

Question

Why do we only study one independent variable at a time?

I know it is the main cause of the whole experiment and that the dependent variable depends on the independent. If you had two independent variables in an experiment, you will not know where your results came from.

Help? Thanks in advanced.

Answer 1

That's right.  If you had two independent variables in an experiment, you would not know whether the difference was due to one, the other, or a bit of both.  For example, imagine you were testing the effectiveness of an experimental drug and you gave someone two different drugs to try.  How would you know which helped (or which gave a negative reaction)?  You need to have just one independent variable.

Answer 2

because you havent gotten to multi-variable calculus yet maybe?  (which is Calc. 3)

Answer 3

You can have several independent variables in an experiment.  But you hold them constant, and look for differences in one at a time.  For example, you can have s*x and education level as two independent variables....dependent variable is "a behavior"...score on a test, something the subject does....you can look for differences in that DV in males vs. females...then between educational levels.  You can be even more refined and look at differences in male college graduates vs. female college graduates vs. male non college graduates vs. female non college.....interaction effects.  But yes, you do statistical analysis looking at differences in one IV, while holding the other IVs constant (because you can have many IVs, if you have a very large sample size).  (college psyc prof)