Sorry
That's Incorrect

Incorrect. This is a tough one because, in a sense,
there is a manipulation of the independent variable.
For example, a single group of patients with a particular
type of infection receives medication X and then is tested
for improvement of the infection.  The manipulation has been
administering the medication. It is not a very good manipulation
because there is no comparison with a group of patients who do not
receive the medication; that is, there are not really two clearly defined
levels of the independent variable, medication X.