7 junio, 2024

Dependent and independent variables: concept and examples

The dependent and independent variables are the two main variables of any experiment or investigation. The independent variable (VI) is the one that changes or is controlled to study its effects on the dependent variable (VD). The dependent is the variable that is investigated and measured.

They can then be seen as cause (independent variable) and effect (dependent variable). The independent is controlled by the experimenter, while the dependent changes in response to the independent. Let’s put an example with the following graph:

This would be the price evolution of the pizzas of an Italian restaurant based on its size. The dependent variable (y) would be the price, while the independent variable (x) would be the size. As can be seen, the small pizza costs 9 Euros, the medium 12 Euros and the family pizza 15 Euros. Therefore, as the size of the pizza increases, it is worth more expensive. That is, the price would depend on the size.

Other examples:

-Effects of fruit consumption on physical resistance. Fruit consumption (VI), physical resistance (VD).

-Effects of sugar consumption on weight. Sugar consumption (VI), weight (VD).

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Independent variable: concept and examples

The independent variable (VI) is the one that changes or is controlled to see its effects on the dependent variable (VD). For example, a study wants to measure the effects of height on weight. Height is VI and weight is VD.

The VI can stand on its own and is not affected by anything the experimenter does or by any other variable within the same experiment; hence its name «independent».

It is the variable that can be systematically handled or manipulated by the experimenter, whose controlled changes have a direct effect on the dependent variable.

Speaking from a mathematical point of view, they are the input elements to the equation or study model and are represented on the abscissa (x) axis in a graph.

In other words, it is the supposed «cause» in the relationship being studied. Generally, a single independent variable is chosen to avoid that several factors simultaneously have an effect on the dependent variable.

If that were to happen, it would be difficult to identify and measure which of the changes in the «independent» variables is causing changes in the observed behavior.

The independent variable is also known as the controlled variable or predictor variable depending on the type of study.

Dependent variable: concept and examples

The dependent variable (VD) is the one that is affected by the independent variable (VD). It is about the effect, about what is measured. For example, in a study you want to measure the influence of the amount of sun that plants receive on their height. The amount of sun is the VI, it is the cause. The height of the plant would be the VD, the effect that is measured.

The dependent variable is represented on the ordinate (y) axis of a graph. The changes observed in this variable are meticulously recorded as a fundamental part of the results of the experiment.

Depending on the type of study, it may also be known as an experimental variable, a measurement variable, or a response variable.

Examples of dependent and independent variables

– A study focuses on knowing the effects of paracetamol when it comes to reducing fever in a patient with coronavirus. The amount of grams of medication consumed daily would be the independent variable (cause), while fever would be the dependent variable (effect).

– The statistics center of a soccer team wants to know the chances of victory that their club has based on the level of the grass on the pitch. The size of the turf will be the independent variable (cause) and the number of wins will be the dependent variable (effect).

– A probiotic dairy products company wants to analyze the effects of an anti-cholesterol yoghurt on its customers based on their habitual consumption. The amount of yogurt eaten each day will be the independent variable (cause), while cholesterol levels would define the dependent variable (effect).

– The director of a school wants to know if the practice of sport influences the grades obtained. The practice of sport would be the independent variable and the grades obtained the dependent variable.

To measure the effects of positive comments from parents to children (VI) on children’s self-esteem (VD).

– Investigate exposure to sunlight (VI) on the levels of happiness of adults and the elderly.

The independent one could be controlled with the exposure time (hours, days, weeks), and the dependent one with a multiple scale where the workers are asked at the end of the day simply how they feel.

– Investigate the effects of the use of social networks (VI) on the school grades of children and adolescents (VD).

– Investigate the influence of the educational level (VI) on the salary level (VD).

Investigate how salt intake (VI) affects blood pressure.

Exercise

An agricultural study wants to examine how fertilizer can influence the growth of avocados. To do this, specific amounts of fertilizer are applied to each tree to determine how much the amount of fertilizer matters.

The data obtained are:

– For 4 mg of fertilizer, avocados grew to 2 cm

– For 6 mg of fertilizer, avocados grew to 5 cm

– For 9 mg of fertilizer, avocados grew to 10 cm

– For 12 mg of fertilizer, avocados grew to 15 cm

Find out what the dependent and independent variable is and make a representative graph of what it would look like.

Solution

In this case, the independent variable (the cause) would be the amount of fertilizers, while the dependent variable (the effect) would be the yield of the size of the avocados. That is, the size of the avocado will depend on the amount of fertilizer applied.

In the study, the objective is to discover how much the use of fertilizers (variable x) will affect the size of the avocados (variable y). From the data obtained from the experiment we can create the following graph.

Themes of interest

Types of variables.

Research techniques.

Types of research.

Research variables.

References

Karl L. Wuensc (2004). Independent Variables and Dependent Variables. East Carolina University-Department of Psychology. Retrieved from core.ecu.edu.
Todd Helmenstine (2017). What Is the Difference Between Independent and Dependent Variables? Independent vs. Dependent Variables. ThoughtCO. Retrieved from thoughtco.com.
Graphic Tutorial what are independent and dependent variables? Retrieved from nces.ed.gov.
Office of Research Integrity (ORI). Case example for Independent and Dependent variables. ORI Curriculum Examples – Basic Research Concepts. Retrieved from ori.hhs.gov.
Science Buddies. Variables in Your Science Fair Project. Retrieved from sciencebuddies.org.

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