Which research method involves manipulating one or more factors and using random assignment of participants?

III. Research that Describes, Predicts, & Explains Behavior (i.e., cause and effect)

The True Experiment: A research method in which an investigator manipulates one or more factors (independent variables) in order to observe the effect on some behavior or mental process (dependent variable).  By randomly assigning participants to groups, other relevant factors are controlled.
     Independent Variable: The factor that is being manipulated by the researchers.  The theoretical "cause" in the cause and effect relationship.
     Dependent Variable: The factor (a behavior or mental process) that is being measured by the researchers.  The variable that is predicted to change in response to the manipulation of the IV.
     Operational Definitions: Specific statements describing how the the IV is manipulated and how the DV is measured.
     Random Assignment: Assigning participants to control and experimental conditions on the basis of chance, thus minimizing pre-existing differences between the groups (i.e., it controls preexisting subject variables.
     Experimental Condition (or Group): The condition of an experiment that exposes participants to the treatment of interest, that is, to one level of the independent variable.
     Control Condition (or Group): The condition of an experiment that contrasts with the experimental condition and serves as a comparison for evaluating the effect of the treatment.

*At the conclusion of an experiment, the mean scores the experimental and control groups receive on the DEPENDENT VARIABLE are COMPARED to determine if a statistically significant difference exists.

Internal Validity: The extent to which one can be confident that the manipulation of the IV caused the changes in the DV.  Internal validity can be assured only if all potential confounding variables have been controlled.

     Random Assignment: Controls pre-existing subject variables.
    Control Group: Controls history, maturation, and testing effects.
     Placebo: An inert substance given to the control group in place of an actual medication.  It controls the Placebo Effect.
              Placebo Effect: Experimental results caused by the subjects' expectations alone.
     Double-Blind Design: An experimental procedure in which both the research participants and the research staff are ignorant (blind) about whether subjects are in the control or experimental groups (commonly used in drug-evaluation studies).  This type of design controls subject and experimenter effects.
              Subject Effects or Biases: Any response by subjects in a study that does not represent how they would normally behave if not under study.  Two powerful subject effects are the placebo effect and the demand characteristics of the study.
              Demand Characteristics: Aspects of the study that suggest to the subjects what type of behavior is expected or desired by the researchers.
              Experimenter Effects or Biases: Any behavior of a researcher that might affect the behavior of the subjects or affect the measurement and recording of the dependent variable.

The Quasi-experimental Design: Designs similar to true experiments, but without all of the control techniques built in (e.g., random assignment may not be used).

See HANDOUTS for more information on research methods.

Ethics: The APA has strict guidelines which must be followed when using both human and animal subjects.  See HANDOUT

How exactly do researchers investigate the human mind and behavior? While there are a number of different research techniques available, the experimental method is one that allows researchers to look at cause-and-effect relationships.

Results obtained through the experimental method are very useful, but they do not prove with 100% certainty that a singular cause will always create a specific effect. Instead, they show the probability that a cause will or will not lead to a particular effect.

The experimental method involves manipulating one variable to determine if this causes changes in another variable. This method relies on controlled research methods and random assignment of study subjects to test a hypothesis.

For example, researchers may want to learn how different visual patterns may impact our perception. Or they might wonder whether certain actions can improve memory. Experiments are conducted on many behavioral topics, some of which include attention, cognition, emotion, memory, perception, and sensation.

The scientific method forms the basis of the experimental method. This is a process used to determine the relationship between two variables—in this case, to explain human behavior.

Positivism is also important in the experimental method. It refers to factual knowledge that is obtained through observation, which is considered to be trustworthy.

When using the experimental method, researchers first identify and define key variables. Then they formulate a hypothesis, manipulate the variables, and collect data on the results. Unrelated or irrelevant variables are carefully controlled to minimize the potential impact on the experiment outcome.

The idea of using experiments to better understand human psychology began toward the end of the nineteenth century. Wilhelm Wundt established the first formal laboratory in 1879.

Wundt is often called the father of experimental psychology. He believed that experiments could help explain how psychology works, and used this approach to study consciousness.

Wundt coined the term "physiological psychology." This is a hybrid of physiology and psychology, or how the body affects the brain.

Other early contributors to the development and evolution of experimental psychology as we know it today include:

• Gustav Fechner (1801-1887), who helped develop procedures for measuring sensations according to the size of the stimulus
• Hermann von Helmholtz (1821-1894), who analyzed philosophical assumptions through research in an attempt to arrive at scientific conclusions
• Franz Brentano (1838-1917), who called for a combination of first-person and third-person research methods when studying psychology
• Georg Elias Müller (1850-1934), who performed an early experiment on attitude which involved the sensory discrimination of weights and revealed how anticipation can affect this discrimination
  

To understand how the experimental method works, it is important to know some key terms.

• Dependent variable: The dependent variable is the effect that the experimenter is measuring. If a researcher was investigating how sleep influences test scores, for example, the test scores would be the dependent variable.
• Independent variable: The independent variable is the variable that the experimenter manipulates. In the previous example, the amount of sleep an individual gets would be the independent variable.
• Hypothesis: A hypothesis is a tentative statement or a guess about the possible relationship between two or more variables. In looking at how sleep influences test scores, the researcher might hypothesize that people who get more sleep will perform better on a math test the following day. The purpose of the experiment, then, is to either support or reject this hypothesis.

Operational definitions are necessary when performing an experiment. When we say that something is an independent or dependent variable, we must have a very clear and specific definition of the meaning and scope of that variable.

Psychologists, like other scientists, use the scientific method when conducting an experiment. The scientific method is a set of procedures and principles that guide how scientists develop research questions, collect data, and come to conclusions.

The five basic steps of the experimental process are:

1. Identifying a problem to study
2. Devising the research protocol
3. Conducting the experiment
4. Analyzing the data collected
5. Sharing the findings (usually in writing or via presentation)

Most psychology students are expected to use the experimental method at some point in their academic careers. Learning how to conduct an experiment is important to understanding how psychologists prove and disprove theories in this field.

There are a few different types of experiments that researchers might use when studying psychology. Each has pros and cons depending on the participants being studied, the hypothesis, and the resources available to conduct the research.

Lab experiments are common in psychology because they allow experimenters more control over the variables. These experiments can also be easier for other researchers to replicate. The drawback of this research type is that what takes place in a lab is not always what takes place in the real world.

Sometimes researchers opt to conduct their experiments in the field. For example, a social psychologist interested in researching prosocial behavior might have a person pretend to faint and observe how long it takes onlookers to respond.

This type of experiment can be a great way to see behavioral responses in realistic settings. But it is more difficult for researchers to control the many variables existing in these settings that could potentially influence the experiment's results.

While lab experiments are known as true experiments, researchers can also utilize a quasi-experiment. Quasi-experiments are often referred to as natural experiments because the researchers do not have true control over the independent variable.

A researcher looking at personality differences and birth order, for example, is not able to manipulate the independent variable in the situation (personality traits). Participants also cannot be randomly assigned because they naturally fall into pre-existing groups based on their birth order.

So why would a researcher use a quasi-experiment? This is a good choice in situations where scientists are interested in studying phenomena in natural, real-world settings. It's also beneficial if there are limits on research funds or time.

Field experiments can be either quasi-experiments or true experiments.

The experimental method can provide insight into human thoughts and behaviors, Researchers use experiments to study many aspects of psychology.

A 2019 study investigated whether splitting attention between electronic devices and classroom lectures had an effect on college students' learning abilities. It found that dividing attention between these two mediums did not affect lecture comprehension. However, it did impact long-term retention of the lecture information, which affected students' exam performance.

An experiment used participants' eye movements and electroencephalogram (EEG) data to better understand cognitive processing differences between experts and novices. It found that experts had higher power in their theta brain waves than novices, suggesting that they also had a higher cognitive load.

A study looked at whether chatting online with a computer via a chatbot changed the positive effects of emotional disclosure often received when talking with an actual human. It found that the effects were the same in both cases.

One experimental study evaluated whether exercise timing impacts information recall. It found that engaging in exercise prior to performing a memory task helped improve participants' short-term memory abilities.

Sometimes researchers use the experimental method to get a bigger-picture view of psychological behaviors and impacts. For example, one 2018 study examined several lab experiments to learn more about the impact of various environmental factors on building occupant perceptions.

A 2020 study set out to determine the role that sensation-seeking plays in political violence. This research found that sensation-seeking individuals have a higher propensity for engaging in political violence. It also found that providing access to a more peaceful, yet still exciting political group helps reduce this effect.

While the experimental method can be a valuable tool for learning more about psychology and its impacts, it also comes with a few pitfalls.

Experiments may produce artificial results, which are difficult to apply to real-world situations. Similarly, researcher bias can impact the data collected. Results may not be able to be reproduced, meaning the results have low reliability.

Since humans are unpredictable and their behavior can be subjective, it can be hard to measure responses in an experiment. In addition, political pressure may alter the results. The subjects may not be a good representation of the population, or groups used may not be comparable.

And finally, since researchers are human too, results may be degraded due to human error.

Every psychological research method has its pros and cons. The experimental method can be helpful for establishing cause and effect, and it's also beneficial when research funds are limited or time is of the essence.

At the same time, it's important to be aware of this method's pitfalls, such as how biases can affect the results or the potential for low reliability. Keeping these in mind can help you review and assess research studies more accurately, giving you a better idea of whether the results can be trusted or if they have limitations.