What kind of research that the researcher manipulates one or more variables and observe the impact on other variables?

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Case Examples for Independent and Dependent Variables
Case Example for Descriptive Study Variables
See if you can identify the variables that are under investigation in the following descriptive study:

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.

When a researcher gives an active medication to one group of people and a placebo, or inactive medication, to another group of people, the independent variable is the medication treatment. Each person's response to the active medication or placebo is called the dependent variable.

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:

In an experimental study looking at classical music exposure and reading ability in children, the researcher divided the children into two groups (Groups A and B). In Group A, the children listened to Mozart for one hour every day for one month. In Group B, parents were instructed to refrain from playing classical music around the child for one month. At the end of the month, all children were given a reading comprehension test. Those who listened to Mozart daily (Group A) scored significantly higher on the reading test. In this case, the reading comprehension test score is the dependent variable and exposure to Mozart’s music is the independent variable. This is because the test score is dependent on whether or not the child listens to Mozart’s music. The independent variable, exposure to Mozart’s music, is independent because it is something that can be manipulated or changed by the researcher.

Example 2:

In a study with a similar design as the previous example, researchers looked at the effects of nutrition on reading ability. In Group A, children ate at least three ounces of dark green vegetables every day for one month. In Group B, children were fed their regular diet. At the end of the month, the children took a reading comprehension test. Those who ate the green vegetables every day for one month (Group A) did not vary in their test scores when compared to Group B.

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?

What is a Dependent Variable?

In an experiment, the independent variable is manipulated and the effects observed. These observed effects are called dependent variables. They are often the hypothesized outcome of manipulating the independent variable.

A change in the dependent variable depends on the independent variable, hence the name. The dependent variable responds to the independent variable, and it’s this relationship that researchers attempt to measure when conducting experiments.

A well-designed experiment normally incorporate one or two independent variables, with every other possible factor eliminated, or controlled. There may be more than two dependent variables in any experiment.

Dependent Variable Examples

A researcher might wish to establish the effect of fertilizer on the rate of plant growth; amount of fertilizer is the independent variable. They could regard growth as height, weight, number of fruits produced, or all of these. A whole range of dependent variables arises from one independent variable.

For an example, consider pharmaceutical trials, where researchers may administer new medicines to participants to determine the optimal dose. The independent variable is how much medicine the participants receive. If the medicine is an antihistamine, the dependent variable might be the severity of allergy symptoms a participant displays, such as red eyes or sneezing.

Here, the researchers might also measure other relevant dependent variables which may turn out to be unwanted side effects of the medicine, such as drowsiness.

In any experimental design, the researcher must determine that there is a definite causal link between the independent and dependent variable.This reduces the risk of 'correlation and causation' errors. Controlled variables are used to reduce the possibility of any other factor influencing changes in the dependent variable, known as confounding variables.

In the above plant growth example, the plants must all be given the same amount of water, or this factor could obscure any link between fertilizer and growth.

For the antihistamine trial, a confounding variable may be that a participant’s symptoms could improve simply with the passage of time. This is addressed with a control group that receives no medicine at all, allowing researchers to compare all groups and isolate only the true effects of the medicine. The participants might also be asked to stop all other medication during the experiment – another possible confounding variable.

The relationship between the independent variable and dependent variable is the basis of most statistical tests, which establish whether there is a significant correlation between the two. The results of these tests allow the researcher to accept or reject the null hypothesis, and draw conclusions.

Independent Variable or Dependent Variable?

It can sometimes be tricky to tell the independent and dependent variable apart. If you’re unsure:

Ask yourself which variable is affecting or influencing which other variable. The variable being affected is likely the dependent variable.
Try to construct a cause-and-effect sentence with the independent variable being the cause and the dependent variable being the effect. For example, “coffee consumption causes increased productivity.” The sentence will not make much sense if you’ve confused the independent and dependent variables: “productivity causes increased coffee consumption.”
Ask which outcome variables you are measuring – these are likely the dependent variables.