Identifying Variables
 Types of Variables
o There are 2 main types of variables:
 Independent Variable: The variable that is changed by the scientist; the ‘I
change’ this variable (what I do to the …)
 Dependent Variable: The variable that might change because of what the
scientist changes – what is being measured -DATA
o Remember: Your hypothesis can TELL you what your variables are!
 Ex. If I drink Mountain Dew before bed, then I will not sleep very much.
 IV: Drinking Mountain Dew
 DV: the amount of sleep
o Practice:
 Use this hypothesis to identify the variables:
 If I leave all the lights on all day, then my electric bill will be
expensive
o IV: ______________________
o DV: ______________________
 If I brush my cat more, then there will be less fur on my furniture
o IV: ______________________
o DV: ______________________
 Now read the following experiment and identify the independent and
dependent variables
 Elizabeth wanted to test if temperature affected how fast milk goes
bad and curdles. She left milk in a room temperature closet, a fridge,
and a oven that was turned on low heat. She then measured how
rotten the milk was after 10 days.
o Hypothesis: IF___________________________________
THEN____________________________________________
o IV: ____________________________________
o DV: ____________________________________
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Puzzle Example
Students of different ages were given the same jigsaw puzzle to put together. They were
timed to see how long it took to finish the puzzle.
Identify the variables in this investigation:
Independent Variable
Dependent Variable
Electromagnetic Example
An investigation was done with an electromagnetic system made from a battery and wire
wrapped around a nail. Different sizes of nails were used. The number of paper clips the
electromagnet could pick up was measured.
Independent Variable
Dependent Variable
Egg Example
The higher the temperature of water, the faster an egg will boil.
Independent Variable
Dependent Variable
Depth Example
The temperature of water was measured at different depths of a pond.
Independent Variable
Dependent Variable
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There are three kinds of variables that you must account for in an experiment. The
independent variable is what you change in the experiment. For instance, if you are
trying to find out how much magnesium radish plants need to grow, your
independent variable might be concentration of magnesium in the nutrient solution.
It is important that you have only one independent variable in your experiment.
The dependent variable is what you measure in the experiment. Unlike the
independent variable, an experiment can have several dependent variables because
variations in the independent variable can have many different effects. Dependent
variables can include qualitative as well as quantitative data.
Any other conditions in the experiment are called controlled variables. You must
keep these conditions constant for all plants in the experiment. Controlled variables
might include light exposure, humidity, pH of solution, ambient noise, etc. If you
change these variables, they become independent variables, and remember that you
cannot have more than one independent variable in a scientific experiment.
The control group is the group of plants in which the independent variable is held at
a "normal" level. The purpose of a control group is to show what would normally
happen and compare it with what happens when you change the independent
variable. This shows if the independent variable is really responsible for your
observations. Be careful not to confuse the control group with the controlled
variables. Remember, the control group is the group in which the independent
variable isn't changed, and the controlled variables are the variables that never
change in any group.
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