Knowing the Variables
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The importance of knowing and controlling the variables cannot be emphasized enough and applies to projects in all categories. This is essentially something that needs to be considered from the very beginning of your project. Pay close attention to variables that are being tested for, versus variables that are being held constant. A control variable is simply a variable that is not being studied. Control variables are held constant so that they do not interfere or influence the outcome of the experiment at hand. Environmental conditions (air pressure, moisture, suspended particles, temperature, time), intelligence or emotional quotients, engineering systems, and social and psychologic variables are examples of variables that must be controlled.
Judges pay close attention to this. They will scrutinize the choice of variables and the method of control.
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How do you know what are the variables?
You have to do research on what it is you are trying to do. Read books, scientific journals, credible online resources, mentors, etc. By reading and understanding more about your idea, you learn about the factors affecting your topic and in doing so you have identified the variables.
How do you control the variables?
This is perhaps the most difficult. Learn more about the factors involved, think of innovative ways to control the variable, consult the literature and your teacher/mentor. This is where scientific journals come to help; someone might have done a similar experiment studying some other variable. You can use relevant part of their experimental approach in order to construct your own procedure (you must reference it though).
Example:
A project testing the growth of plants under blue, green and red colours of light selected through filters (coloured opaque sheets surrounding the plant) against plants grown under normal light consisting of the entire spectrum. What are the variables?
After thinking and researching we find that there are two kinds of factors: Genetic and Environmental:
- Genetic factor
- Genetic Makeup
- Environmental factors:
- Light
- Temperature
- Humidity
- Water (it’s pH)
- Soil composition
- Air composition
There might be others, but these are enough for the purpose here.
Controlling the variables:
The variable being studied is light, which means that we need to “control” all the other variables so that we can say with some confidence that the difference which we might find is due to the variation in colour of the light and compare it to the normal plant.
How we do we control these variables:
Genetic Makeup:
- Two plants of the same species from Asia and Canada would most certainly have a different genetic makeup based on their evolution. One might grow more in higher temperature than the other. Therefore, it is important to have the plants with the most identical genetic makeup. This would be when the two plants are the progeny of the same parents.
Temperature:
- Keeping the temperature constant is the key. If the temperature in which the plants are being grown is different, then the colour of the light would not be the only factor being varied.
Humidity:
- Similar to temperature, the humidity must be kept constant.
Water:
- The amount of water given to all the plants must be the same. It should have the same composition and pH.
Soil and Air composition:
- The soil and air composition must be constant.
A possible way of doing this experiment would be in a greenhouse, but it could also be done using progeny of two parents in the same room at home, germinating at the same time in the same soil mixture, monitoring and keeping track of humidity and temperature while providing the plants with the same amount of water. The light provided could be from artificial lamps with the same power. Plants without colour filters will also be grown under the same conditions.
With keeping these factors constant, you might think that you have taken enough “precautions,” but you still need to do replicates and use randomization in order to do the proper statistical analysis such as the Chi-square test and the test hypothesis to prove if there are significant differences between plants grown in blue, green, red and normal light. (For this statistics, refer to the “letting the numbers talk” section).
Is this good enough? I mentioned the key is being “critical.” Well, there are more factors to consider. Is all the light the plant getting all of a particular colour? Is each plant getting the same amount of light? There is still individual genetic variation present, have you taken enough care to rule it out?
There could be other improvements to this experiment but the point is to control the variables.
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