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The independent variable is one of the two main variables that are taken into account in any scientific experiment. The independent variable is the one that the researcher has under his control and whose values he sets according to his own criteria in order to establish its effect on the other variables . As its name indicates, the independent variable does not depend on the value of any other variable in the experiment, but rather, it is the one that affects the outcome and behavior of the other variables.
The independent variable represents what the researcher considers to be the cause of a phenomenon, while another variable, called the dependent variable, represents the effect.
For example, when studying weight gain in adolescents, the average number of calories they eat per day is related to the individual’s weight.
In this case, it is easy to see that the cause of weight gain is the intake of a high amount of calories, and not the other way around. For this reason, it is concluded that calorie intake is the cause of the phenomenon and, therefore, the independent variable, while weight, which depends on calorie intake, is the dependent variable.
Characteristics of the independent variable
The following seven characteristics allow you to easily identify which is the independent variable(s) in an experiment:
- Within certain limits, they are variables that can be controlled by the researcher at will.
- They are also called controlled variables, manipulated variables, or explanatory variables.
- Its value does not depend on that of any other variable. That is why they are called independent variables.
- It directly affects the outcome of an experiment.
- They can represent the cause of a phenomenon.
- They can exist without the dependent variables.
- In graphs, they are always placed on the X axis (the abscissa axis).
Types of independent variables
Both the dependent and the independent variable can be of two types:
Quantitative variables
Quantitative independent variables are those whose values can be represented by numbers. They can be discrete (such as the number of push-ups an athlete does per week) or continuous (such as height, weight, walking speed, etc.).
qualitative variables
They are those that represent qualities. These variables cannot be represented by numbers. Qualitative independent variables can also be of two types: nominal (for example, the brand of soft drink that a person usually drinks) or ordinal, if their values establish some kind of order or hierarchy (for example, educational level, established height such as low, medium and high, etc.).
The independent variable, the hypothesis and the scientific method
In all scientific experiments one seeks to establish or confirm cause and effect relationships associated with the phenomenon being studied. To achieve these objectives, the researcher relies on the scientific method, which is a series of logical steps that begin with a question that a researcher asks about a phenomenon or system of interest.
After studying said system looking for the answer to your question, a hypothesis or supposition about the causes of the observed phenomenon is raised, and then an experiment is designed to verify or rule out said hypothesis.
It is during the statement of the hypothesis and the design of the experiment when the dependent and independent variables appear.
Example:
If, in studying birds, a researcher hypothesizes that day length influences plumage color, then the researcher has already made a decision about what he considers to be cause and effect, and therefore has already made the decision. established what the independent variable is. In this case, it is the length of the day.
It is now the researcher’s job to design an experiment in which he can somehow manipulate day length for the birds he wishes to study, and determine whether or not this independent variable affects plumage color.
Examples of Independent Variables
As mentioned above, what the independent variable is depends on the study being conducted. The same variable can be the independent one in one study and the dependent one in another.
For example, tall stature may be the consequence of a good diet, in which case diet would be the independent variable and height the dependent variable. On the other hand, height may be the cause of a basketball player’s success, in which case height would be the independent variable and sporting success the dependent variable.
With that said, here are some examples of variables that are often the cause of different phenomena:
- The hours dedicated to the study of a subject.
- The number of hours per week dedicated to physical exercise.
- The number of followers of an influencer on a social network.
- The temperature at which a chemical reaction takes place.
- The concentration of a drug in the bloodstream.
Examples of how to identify the independent variable
In addition to these independent variable examples mentioned above, here are two examples to illustrate how to tell what the independent variable is in a real world situation.
The melted cheese company
At a company that produces spreadable processed cheese, the research and development department is working on a new product. They decide to determine what is the optimal amount of a bacon flavoring to add to the mix and to do this, they recruit a group of volunteers who will be given samples with different amounts of the flavoring and who will report how much they like them. liked the new product in terms of color, taste, texture, and appearance.
In this case, the variable that the researchers are controlling for is the amount of flavoring added, therefore this is the independent variable. All other variables (taste, color, texture, and appearance) are a consequence of the amount of flavoring added, so they are dependent variables.
A study on headphones
An otolaryngologist decides to carry out a study to determine if the type of earphones or headphones used to listen to music has an effect on the incidence of outer ear infections. To do this, he selects a large sample of people who are used to listening to music on a daily basis, but with different types of headphones. Some use headphones, others use in-ear headphones , etc., and others do not usually use headphones (control group).
In this case, it can be seen that the ENT hypothesis is that earphone type affects the incidence of ear infections, so earphone type is the independent variable in this study.
References
- Britannica, T. Editors of Encyclopaedia (2020, January 16). Scientific method . Encyclopedia Britannica. Retrieved from https://www.britannica.com/science/scientific-method
- Raymond, P., Ricardo, & Johnson. (2021, March 16). Research Methods . Retrieved from https://espanol.libretexts.org/@go/page/49897
- Salinas, PJ (2010). SCIENTIFIC RESEARCH METHODOLOGY . Merida, Venezuela. University of the Andes.
