- You know, what were your controls? This really is one of the
fundamental question of experimental biology that, are not trivial and
really have to be thought through very carefully. Effectively, a
control is subtracting or adding a critical variable. A negative
control is maintaining all the other variables constant but removing
the one key variable that you want to test in your experiment.

- So a negative control is where that outcome is negative. So it's the
absence of something. It's the lack of some effect. So if you think
about a drug trial where you have, a drug of interest, that you're
looking to see if there is an effect. You don't know what the outcome
is going to be, a negative control for that would be the placebo. So
you're administering something that you know should have no effect
whatsoever, and that lack of effect is the negative control.

- A positive control is an example of adding another variable, in this
case, likely a known variable that you would expect to produce a
particular effect.

- In our experiment our positive control was a cell line that was
expressing both HER‐2, and HER-3. The regular HER-2 amplified breast
cancer cells. So those cells were our positive control because they
were generating tumors. So they were giving us to outcome that we were
expecting for those cells. Were telling us that our experiment was
being performed properly.

- So to me, very generally when someone says this is my control it
means this is a condition where I have an expected results, and if
there's a deviation from that result that tells me that there is some
problem, some aberration with the experiment. And without doing
controls to check for those possibilities, your data are a lot more
difficult to interpret.

- Imagine, we only put the knockout HER-3 cells and we waited four
months to see if the tumors develop. And lets say, that after one
year, there was no tumor development. So we will have concluded that
those HER-3 knockout cells were not able to produce tumors. Yes,
because we didn't have our proper control. We will have said that
something happened during injection, or for whatever reason the mice
were not developing tumors. So it's very important to have a positive
control because that will allow you to make the proper conclusion with
the cells that you are testing.

- These controls are also useful to see if there are any other
confounding variables that may be affecting the results. You know, in
those cases one often then has to like, search for what the possible
source of that experimental result might be. That is often then like a
search through all of the variables of an experiment, to see what
might be producing a particular outcome. Or in many cases the lack of
a particular outcome. I think that the really main purpose of control,
is to help you interpret the data. If you lack some key experiment to
tell you how to interpret it, that's what you really need the control
for.