We're going to spend a lot of time dealing
with the scientific method, especially at
the beginning of the year, and designing controlled
experiments. That whole idea of how you set
set up an experiment is just as important - if not more important - than the results. 
Because if you don't set it up right, it doesn't really matter what your results are. So let's talk
about the different aspects of a controlled
experiment. A controlled experiment is one
in which you have a control group and experimental
groups, and the control group basically acts
as a baseline for comparison. So what does
that mean? Basically it means that in the
two different groups, in this case the control
group and the experimental group, one group
- the control group - is kind of left alone
in terms of the one thing we're studying,
whereas the experimental group is where you're
going to be changing something. So in this
case, it looks like we have some plants, maybe
you're changing the amount of fertilizer or
sunlight or water. So that's a controlled
experiment. I want to talk more about this
idea of changing things. These things that
we change, those are known as variables, and
there are two really important terms that
we will use a lot that I want you to understand,
two really important different types of variables.
The first one is the independent variable,
which a lot of times we just abbreviate IV,
you'll see that a lot, independent variable.
This is the one variable that is changed or
manipulated in the experiment. So if you think
back to the plants on the previous slide,
if we were changing the amount of fertilizer,
that is the independent variable - the one
thing you change. The control group, you don't
give it the independent variable, or you keep
it as they baseline, the same, maybe no fertilizer,
and then the experimental group, or you might
have multiple experimental groups, you change
the amount of fertilizer that's given. This
leads us to our second variable, which is
the dependent variable, which - you guessed
it - is oftentimes abbreviated DV. The dependent
variable is what we're measuring. It's the
factor that we are most concerned with as
scientists, what we're going to be writing
down and recording. The dependent variable
is affected by the independent variable. So
if we think about those plants, the dependent
variable might be the plant height, for example.
You would measure the plant height each day
and see if the amount of fertilizer that's
given, or the independent variable, affects
the height of the plant, or the dependent
variable. Everything else that you don't change,
those are the constants. All of the other
potential variables that remain the same.
So if you think about the plant experiment,
the soil, the type of plant, sunlight, water,
etc., all of those would have to be the same.
You change one thing, and the one thing you
change is the independent variable.
