A variable is something that can have different values, such as weight, height, or eye color, as opposed to a constant that has only one value, such as the speed of light.
The types of variables are determined by the data it represents. For example, weight is a quantitative variable when it is expressed in numbers such as grams or kilograms of an object. Whereas if it is presented in terms of “heavy” or “light,” it would be a qualitative variable, because it presents a quality.
We use different types of variables in mathematics, statistics, and scientific research. Let’s see.
Continuous quantitative variable
A continuous quantitative variable is any variable represented by numbers that can be expressed by fractions or decimals such as temperature, where we find values like 37 ºC, 37.5ºC or 38.5ºC.
Other examples of variables are:
- The levels of a compound in the blood.: the blood sugar levels of a person with diabetes during a day may be 7.5 mM, 8.3 mM or 5.0 mM.
- The measurement of atmospheric pressureAt 0 meters above sea level the atmospheric pressure is equal to 1 atm and at 1000 meters above sea level it is equal to 0.887 atm.
- The mass of an object: avocados from a tree can measure 200.5 grams, 201 grams or 205.2 grams.
- The length of an object: the height of trees in a park.
Discrete quantitative variable
A discrete quantitative variable can only take integral values, i.e. 1, 2 or 555, but not 1.5 or 2.25. Examples of this type of variable are:
- The number of times something happens: the number of times it rained each month in the year 2020 in Bogota.
- The number of times someone assumes a certain behavior.The number of times people over the age of 50 participate in a marathon.
- The number of people or beings in a groupThe number of students in a classroom can only be an integral value, there cannot be a fraction of a student.
- The number of objects in a placeThe number of chairs or books in each classroom in a school.
Dichotomous qualitative variable.
The dichotomous qualitative variable is a non-numerical data that presents an observable quality, property or condition, which only presents two values. For example:
- Ehe verdict of a jury: “guilty” or “not guilty”.
- Sex: “male” or “female”.
- The result of an antigen test: “positive” or “negative”.
- Presence of a condition.: “present” or “absent”.
- The type of hospital: “public” or “private”.
Categorical or nominal qualitative variable.
It is the non-numerical variable that presents three or more categories. For example:
- Affinity for a teamIn Mexican soccer you can be a fan of “Atlas Fútbol Club”, “Club América” or “Club León”.
- Olympic sportsOlympic sports: “swimming”, “volleyball”, “athletics”, “fencing” or “gymnastics”.
- The states of matter: “solid”, “liquid” or “gaseous”.
- University careersBiology”, “law”, “medicine”, “nursing” or “economics”.
Ordinal variables
Values can be ordered, from least to greatest, from most important to least important, from first to last, etc. We observe this type of variable in:
- Social class: “lower class”, “middle class” or “upper class”.
- Socioeconomic levelA/B (rich class), C+ (upper middle class), C (middle class), D+ (lower middle class), D (poor class), E (extreme poverty).
- Language proficiency: “basic”, “intermediate” or “advanced”.
- Grades of a school: first grade, second grade, third grade, etc.
Independent variable
The independent variable is a variable that occurs without the need for another variable. In science, it is the variable manipulated or controlled by the researcher. That is, values can be attributed to it at will within certain limits. For example, in the study of the effects of a drug, the independent variable can be qualitative if there is a control group without drug and a group with treatment.
In general, scientific studies focus on examining the effects of an independent variable. In one study, the impact of five intensities of a magnetic field on barley plants was analyzed. In this case, the independent variable was the intensity of the magnetic field.
Dependent variable
Dependent variable is a variable that is a consequence of another variable. For example, the height of children is a dependent variable of age. A 10-year-old child is taller than a 5-year-old child.
The dependent variable is the measure of the effect of the independent variable. In one study, waist circumference was measured in two groups of women, a control group and a group that practiced dance therapy for eight weeks. The dependent variable is waist circumference, while the dance regimen is the independent variable.
The easiest way to identify a dependent variable is to detect the effect or consequence of something, i.e., the independent variable that is the cause. As in the previous case, the dance practice is the cause or independent variable and the consequence is on the waist measurement or dependent variable.
While the independent variable is manipulated or fixed, the dependent variable is measured or recorded.
Extraneous independent variable
These are those independent variables that are unrelated to the purpose of the study, but may affect the dependent variables.
An example of an extraneous variable is intelligence in a study of the effects of eating breakfast and the results of a math test in a group of students. The independent variable is assumed to be eating or not eating breakfast before taking a math test. The results of the test would be the dependent variable, however, in this case, the intelligence of each child could influence the outcome.
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References
Ercan, I, et al. (2021) Magnetic field effects on the magnetic properties, germination, chlorophyll fluorescence, and nutrient content of barley (Hordeum vulgare L.) Plant Physiol. Biochem. 170:36-48. doi: 10.1016/j.plaphy.2021.11.033.
Hernández-Sampieri, R., Fernández Collado, C., Baptista Lucio, P. (2014) Research methodology 6th ed. McGraw-Hill. Mexico.
Marczyk, G., DeMatteo, D., Festinger, D. (2005) Essentials of research design and methodology. Jon Wiley & Sons. New Jersey.
