Question

Check your understanding of the experimental method by identifying the independent variable (IV) and dependent variable (DV) in the following investigations. Note that one study has two IVs and another has two DVs. You'll find the answers in Appendix A in the back of the book. A researcher is interested in how heart rate and blood pressure are affected by viewing a violent film sequence as opposed to a nonviolent film sequence. \(\mathrm{IV}\)______________________________________________ \(\mathrm{DV}\)_____________________________________________

Short answer

Answer: The independent variable (IV) is the type of film sequence (violent or nonviolent). The dependent variables (DVs) are heart rate and blood pressure.

Step-by-step solution

Identify the Independent Variable (IV)

In this experiment, the researcher is interested in studying the effects of viewing violent and nonviolent film sequences. The manipulation being done by the researcher is the type of film sequence the participants are watching (violent or nonviolent). Therefore, the Independent Variable (IV) is the type of film sequence (violent or nonviolent).

Identify the Dependent Variable(s) (DV)

The researcher is measuring two outcomes in this experiment: heart rate and blood pressure. These are the variables that the researcher expects to be affected by the manipulated variable (IV). So, in this case, there are two Dependent Variables (DVs) - heart rate and blood pressure.

Key concepts

Independent Variable

In the context of experimental psychology, the independent variable (IV) is the element that the researcher manipulates to determine if it causes any change in the behavior or response being measured. It's the presumed cause in a cause-effect hypothesis.

For instance, in the given exercise, the type of film sequence—whether it's violent or nonviolent—is the independent variable. The researcher has control over this variable and changes it to observe the effects on the dependent variables. It's essential to clearly define the independent variable, as it is a central piece of the experimental method that allows the psychologist to make causal inferences about the relationship between variables.

When designing an experiment, one must also consider control over other factors that might influence the results. These are known as extraneous variables, and managing them is critical to ensure that any observed effects can truly be attributed to the manipulation of the independent variable.

Dependent Variable

The dependent variable (DV) in an experiment is the variable that is being measured or tested. It is expected to change as a result of the experimental manipulation of the independent variable. Essentially, it is the effect or outcome that the research is interested in understanding.

In the exercise, heart rate and blood pressure serve as dependent variables. They are the physiological responses that the researcher predicts will be affected by watching different types of film sequences. Accurate and reliable measurement of the dependent variables is crucial, as it reflects the potential impact of the independent variable. Additionally, having more than one dependent variable can provide a more comprehensive understanding of the experimental manipulation's effects.

Experimental Manipulation

The term experimental manipulation refers to the deliberate alteration of the independent variable by the researcher to observe what effect it has on the dependent variable. This is the core of the experimental method, which differentiates it from observational studies where variables are not deliberately changed.

In our example, experimental manipulation involves presenting participants with either a violent or nonviolent film sequence. The goal is to create distinctly different conditions for comparison. Experimental manipulation is designed carefully to ensure that it is the only significant difference between conditions, which helps in establishing cause and effect relationships.

Outcome Measurement

Lastly, outcome measurement involves quantifying the changes observed in the dependent variable(s) in response to the experimental manipulation. The method of measurement should be reliable and valid, meaning it consistently provides accurate data that truly represents the variable of interest.

In relation to our exercise, outcome measurements would include how the heart rate and blood pressure of participants change when exposed to either type of film. The techniques to measure these outcomes could be heart rate monitors and blood pressure cuffs. If these tools are precise and calibrated correctly, the data they produce can lead to meaningful conclusions about the effects of violent content on physiological responses.