The purpose of all research is to describe and explain variance in the world. Variance is simply the difference; that is, variation that occurs naturally in the world or change that we create as a result of a manipulation. Variables are names that are given to the variance we wish to explain.
A variable is either a result of some force or is itself the force that causes a change in another variable. In experiments, these are called dependent and independent variables respectively.
This could be many things depending upon what the medication is for, such as high blood pressure or muscle pain. Therefore, in experiments, a researcher manipulates an independent variable to determine if it causes a change in the dependent variable.
As we learned earlier in a descriptive study, variables are not manipulated. They are observed as they naturally occur and then associations between variables are studied. In a way, all the variables in descriptive studies are dependent variables because they are studied in relation to all the other variables that exist in the setting where the research is taking place. However, in descriptive studies, variables are not discussed using the terms "independent" or "dependent." Instead, the names of the variables are used when discussing the study. For example, there is more diabetes in people of Native American heritage than people who come from Eastern Europe. In a descriptive study, the researcher would examine how diabetes (a variable) is related to a person's genetic heritage (another variable).
Definition: A variable is either a result of some force or it is the force that causes a change in another variable. In experiments, these are called dependent and independent variables respectively.
Case Examples for Independent and Dependent Variables
Example 1:
Example 2:
- In the second example what is the independent variable? Why?
- In the second example, what is the dependent variable? Why?
- Identify which variables are dependent and independent in the following examples:
Example:
- Physical activity and weight loss
Dependent Variable: weight loss
Independent Variable: physical activity
- Positive feedback and self confidence
Dependent Variable:
Independent Variable:
- Headache and aspirin
Dependent Variable:
Independent Variable:
- Muscle mass and weight-training
Dependent Variable:
Independent Variable:
- Calcium consumption and bone density
Dependent Variable:
Independent Variable:
- Blood pressure and salt intake
Dependent Variable:
Independent Variable:
Variables are important to understand because they are the basic units of the information studied and interpreted in research studies. Researchers carefully analyze and interpret the value(s) of each variable to make sense of how things relate to each other in a descriptive study or what has happened in an experiment.
Definition: Variables are characteristics studied in research that can take on different values (e.g., weight, height, exposure to a substance, demographics (i.e., where you live, your ethnicity, how much income you have, medical background).
Case Example for Descriptive Study Variables
See if you can identify the variables that are under investigation in the following descriptive study:
Many children who live in the Bronx, a borough of New York City, are developing asthma. In a descriptive study investigating this problem, parents whose children have asthma are asked about whether they smoke around their child, whether they live near a freeway, whether their child regularly sees a healthcare provider, their family income level and also if there is a history in their family of asthma. Prior research has shown that these factors may have an influence on the development of asthma in children.
- What are the variables that are under investigation in this study?
- If you were the researcher, what other variables would you study to see if it may contribute to developing asthma? Why?
- Given the variables presented in the example and the variables that you thought of, why would these variables be useful to the researcher?
Before you start your experiment, you need to have a clear definition of, and strategy for, how each variable will be measured and recorded. This process is called variable operationalization.
For example, you are interested in studying attitudes towards food, visual attention, and food choice. In your first study, your objective is to investigate “the effect of personal health goals on visual attention to different food groups”.
The first part of your objective, “the effect of personal health goals…”, contains an independent variable. To operationalize it you need to ask yourself the following questions: What is a personal health goal? Can you quantify and measure it? Can you break it down into distinct categories? How will you collect and record its value? Due to the nature of this term, your variable will most likely be composed of two or more categories (e.g. lose weight, keep weight, gain weight etc.) and its value recorded by means of a questionnaire or interview. Notice that in this example, the independent variable is also an intrinsic attribute of a participant and thus particular to that individual, as a result, this variable can also be classified as a participant variable.
The next part of your study objective “…on visual attention to different food groups”, contains your dependent variable. Once again, you will need to ask yourself the following questions: What is visual attention? How do I measure it? How is food grouped? How will we represent the different groups in the stimuli? Which grouping strategy is relevant to my objective? The term “visual attention to” can be operationalized into one or more relevant visual behavior measures that can be quantified and measured continuously. For example, eye tracking metrics like fixation duration, fixation count, and dwell time can provide you with information about the visual engagement and bias towards different items in your stimulus. The “… different food groups” term will most likely be operationalized as food types aggregated into categories (e.g. vegetables, red meat, dairy) and displayed on an image stimulus. Since you are manipulating the content of the stimulus and the manipulation affects the context in which the behavior occurs as well as the viewing behavior itself, your stimulus categories will be part of your set of independent variables and simultaneously a stimulus variable.