
Can you explain to me what an independent variable is? 
Question Date: 20140925   Answer 1:
It sounds like you are starting to learn the
scientific method!
You can think of an independent variable is the
variable that is being varied by you the
experimenter or scientist; it is the
input/"cause"/the tunable variable. A dependent
variable is the response/output/"effect".
There is also the control variable, which are
variables that stay constant throughout. You
generally have only one independent variable and
many control variables so that you can properly
disentangle cause and effect.
A simple example might be say you want to know
if a certain brand of fertilizer helps your crops
grow. You want to see how much fertilizer you need
for optimal growth without using too much. What is
the independent and dependent variable?
(Highlight below for the answer!)
The independent variable is the amount of
fertilizer you put on the crop. It is the variable
that you, as the tester, vary yourself. The
dependent variable is how much your crop grows.
What about the control? It is the crop you choose
to use the fertilizer on (e.g., corn, wheat,
peas). Certainly, comparing the influence of
fertilizer between corn and peas would not
definitely tell you whether the fertilizer is
effective; if you compared two different crops,
you would have other confounding variables out of
your control, so you want to test it only on one
crop at a time.
I put cause and effect in quotes because you
may run into one of many cause/effect fallacies
(or mistaken beliefs). It is possible (and often
happens in research) where you plot what you think
is an independent and its dependent variable, but
the reality is quite different! There are two
common types spurious relationships and spurious
correlations. A spurious relationship is one in
which a direct cause/effect relationship is
concluded incorrectly when in fact there is a
lurking or hidden variable unaccounted for. One
commonly cited example is say you find an increase
of death by drownings and ice cream sales. It
would be incorrect to infer that eating more ice
cream causes more drownings, or vice versa. The
lurking variable that can explain both is hot
weather (i.e., people eat more ice cream and go
swimming more to cool down). A spurious
correlation is incorrectly inferring the extent of
how related two variables are (not necessarily a
cause/effect relation, but something used often in
statistics). Here is a website that illustrates
quite ridiculous correlations (a pet project of a
graduate student), emphasizing that correlation is
not causation.
You can find more examples of differentiating
between dependent and independent variables here
at the Kahn Academy. It's a great resource with
short video clips and practice exercises on a
variety of topics. I'll also include these Java
applets in physics, chemistry, math, and more from
the University of Colorado Boulder where the
independent variables are actually nobs you can
tune yourself to see the response!
Hope this helps!
Best,
  Answer 2:
A dependent variable relies (depends) on other
variables to get its value. An independent
variable doesn't rely on any others to get its
value. Think of if you were looking at how
temperature changed with the time of day. It's
hotter in the middle of the day than at either
morning or night. So, the temperature depends on
the time. So, the temperature is dependent, and
the time is independent. If you're looking at a
graph, the independent variable is generally on
the horizontal axis. Also, when you're looking at
an equation, the independent variable is usually
on the side that has other numbers and arithmetic.
So if you have y = 3x + 2, x is
independent since
y depends on it and is isolated.
Sometimes, to
tell which is independent or dependent the
equation will be written like y(x) = 3x +
2. This
y(x) means y(depends on x) and x is
independent.
I
hope this helps! It took me a long time to get
this figured out myself, at least until high
school.
  Answer 3:
The short answer is that you can control an
independent variable directly, but you can’t for a
dependent variable.
Imagine you are heating up a
pot of water on the stove. You can move the dial
to different heat levels; this is an independent
variable. However, the temperature in the pot of
water is a result of you turning a dial so you
can’t control it directly. This makes the
temperature of the water a dependent
variable.
As
an experiment you might start with a pot of water
at room temperature and heat it up on the stove.
You could set the dial to low, medium or high and
measure the temperature. So your independent
variable could take on the values low, medium or
high. But the temperature could take on many
values and if you repeated the experiment multiple
times, you would find that the temperature would
be slightly different every time. What makes the
dial position an independent variable is that you
know completely which values it can take on since
you set them.
  Answer 4:
Usually we talk about independent and dependent
variables with experiments or equations.
An
independent variable is the variable that we
change in experiments or equations. Usually this
is the "X" axis of a graph. The dependent variable
is the result of the experiment or equation.
Imagine a simple experiment:
You want to see how far you can throw rocks. So
you find rocks of different sizes and throw them.
You notice that you can throw lighter rocks
farther than heavier rocks.
In this case, the independent variable is how
heavy the rock is. This is what you are changing
in the experiment.
The result of the experiment (how far you throw
the rocks) depends on how heavy the rocks are. So
we say that how far you throw it is the "dependent
variable"
When we make graphs, we normally put the
independent variable on the "xaxis" and the
dependent variable on the "yaxis."
  Answer 5:
The independent variable is a
variable that does not depend on other variables.
It has no other variables that are causing it
(although it may be causing other, dependent,
variables, itself).
It's also a convention of how you draw graphs 
the independent variable is usually on the
horizontal (x) axis, while the dependent variable
is usually on the vertical (y) axis.
  Answer 6:
Independent variables are variables that
represent "inputs" that you can change to
see if there is an effect. It may be helpful at
least very superficially to think about cause and
effect statements when you are first trying to
distinguish between independent variables and
dependent variables. For example: "If I give a
plant water, then will I see growth in the plant?"
Here, the independent variable is giving plant
water (the "cause" part of the sentence). You can
choose to give the plant water or not.
The dependent variable is the growth in the
plant. Your choice of giving the plant water or
not results in some effect in the growth of the
plant. I hope that helps!
  Answer 7:
And independent variable is something that
you control, on purpose. You choose to change
the independent variable, to see what the effect
is on something else, called the dependent
variable.
For example, if you wanted to see how the
temperature changes as a function of season, the
month could be the independent variable, and the
temperature would be the dependent variable, or
the parameter that _depends_ on the month (the
independent variable). There could be many
dependent parameters for any independent parameter
you choose.
For example, if you chose someone's age as an
independent variable (you're going to look at a
population and see how things change with the age
group you look at), you could pick just about any
dependent variable you want: intelligence (do
people get smarter as they get older?), height (do
people grow as they get older?), weight (do people
get heavier as they get older?), and so on.
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