1.3 Types of variables and their roles in experiments
3 min read•august 7, 2024
Variables are the building blocks of experiments. They come in different types, each playing a unique role. Independent variables are manipulated by researchers, while dependent variables are measured in response. Understanding these distinctions is crucial for designing effective experiments.
are held constant to isolate the effect of independent variables. can muddy results if not accounted for. Moderating and help explain the nuances of relationships between variables. Recognizing these roles enhances experimental design and interpretation.
Types of Variables
Independent and Dependent Variables
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is the variable that is manipulated or changed by the researcher
Independent variable is the presumed cause in an experiment
is the variable that is measured or observed in response to the independent variable
Dependent variable is the presumed effect in an experiment
In a study on the effect of fertilizer on plant growth, the amount of fertilizer would be the independent variable (manipulated by researcher) and plant height would be the dependent variable (measured in response)
Categorical and Continuous Variables
are variables that can be divided into distinct categories or groups
Categorical variables can be nominal (categories with no inherent order, such as eye color) or ordinal (categories with a natural order, such as rankings)
are variables that can take on any value within a certain range
Continuous variables are often measured on a scale, such as height, weight, or temperature
In a survey about favorite ice cream flavors, flavor would be a categorical variable (distinct categories like vanilla, chocolate, strawberry) while rating of enjoyment on a scale from 1-10 would be a continuous variable
Control and Confounding Variables
Control Variables
Control variables are variables that are held constant throughout an experiment to minimize their effect on the dependent variable
Researchers control these variables to isolate the effect of the independent variable on the dependent variable
Control variables help to ensure that any changes in the dependent variable are due to the manipulation of the independent variable and not some other factor
In an experiment on the effect of light on plant growth, temperature and soil type would be control variables (kept the same for all plants) to isolate the effect of light
Confounding and Extraneous Variables
Confounding variables are variables that are related to both the independent and dependent variables, making it difficult to determine the true effect of the independent variable
Confounding variables can lead to misleading conclusions if not accounted for in the experimental design
are any other variables that may affect the dependent variable but are not of primary interest in the study
Researchers try to minimize the influence of extraneous variables through control and
In a study on the effect of a new drug on blood pressure, age could be a (older people tend to have higher blood pressure and may respond differently to the drug) while noise level in the testing environment would be an extraneous variable
Interacting Variables
Moderating Variables
are variables that affect the strength or direction of the relationship between the independent and dependent variables
Moderating variables can enhance, reduce, or change the effect of the independent variable on the dependent variable
Researchers often study moderating variables to understand when or for whom an effect is strongest
In a study on the effect of stress on job performance, coping skills could be a moderating variable (people with better coping skills may perform better under stress compared to those with poor coping skills)
Mediating Variables
Mediating variables are variables that explain how or why an independent variable affects a dependent variable
Mediating variables are the mechanism through which the independent variable influences the dependent variable
Mediating variables are often studied to understand the underlying process or pathway of an effect
In a study on the effect of education on income, job skills could be a (education leads to better job skills, which in turn leads to higher income)