A social psychologist wants to determine if the number of bystanders present during an emergency affects how long it takes for an individual to help. The psychologist stages an emergency in a public space and systematically varies whether there are one, three, or ten other people present. The researcher then measures the time it takes for a participant to intervene and offer assistance. In this experiment, what is the dependent variable?

An experiment can investigate how technology use in the classroom affects learning by comparing note-taking methods. In this scenario, the independent variable is the type of note-taking by participants, such as using a laptop versus writing by hand. The dependent variable is the learning exhibited by participants, measured by their performance on an assessment to evaluate the impact of the independent variable.

Example of an Experiment: Note-Taking Method and Learning Performance

In experimental research, an extraneous variable is any factor that varies within the context of a study other than the specific independent and dependent variables being investigated. These variables pose a significant problem because many of them are likely to influence the dependent variable. If these outside factors fluctuate, they introduce competing influences that make it difficult to separate the true effect of the independent variable from the effects of the extraneous variables.

Extraneous Variable

A time series is a set of measurements of a quantitative variable taken at sequential intervals over a continuous period of time. This approach allows researchers to track trends and ongoing changes within a specific domain, such as recording a factory's weekly worker productivity over an entire year.

Time Series

A confounding variable is an extraneous variable that differs on average across levels of the independent variable, meaning it varies systematically alongside it. Because this variable differs systematically across conditions just like the independent variable, it provides a plausible alternative explanation for any observed difference in the dependent variable, making it difficult to establish a clear cause-and-effect relationship. For instance, if an extraneous variable like intelligence is substantially lower in one group than another, it becomes a confounder that confuses the results.

Confounding Variable

Internal validity indicates the degree to which an empirical study's design justifies the conclusion that changes in the independent variable directly caused the observed differences in the dependent variable. Experimental research designs typically achieve high internal validity because they involve deliberately manipulating an independent variable while rigorously controlling for extraneous variables, thereby eliminating alternative causal explanations. For instance, in the Darley and Latané experiment, the rigorous manipulation of the number of perceived bystanders isolated this independent variable as the direct cause of differences in helping behavior. In contrast, non-experimental correlational designs exhibit low internal validity; for example, a statistical relationship between regular exercise and happiness cannot confirm that exercise causes happiness, as other factors or reverse causation might explain the link.

Internal Validity

In experimental research, a null result occurs when the collected data reveal no statistically significant effect of the manipulation of the independent variable on the dependent variable.

Null Result

Non-experimental research is a broad category of research methodologies defined by the lack of manipulation of an independent variable. Instead of controlling factors, researchers simply measure variables as they naturally occur in real-world or laboratory settings. Although experimental research can provide strong evidence that changes in an independent variable cause differences in a dependent variable, non-experimental research generally cannot. Despite this inability to draw causal conclusions, non-experimental research is still considered extremely important and is utilized in cases where experimental research cannot be carried out.

Non-Experimental Research

In an experimental study, which of the following best describes the dependent variable?

A dependent variable is the factor in an experiment that represents the presumed effect within a causal relationship. It is the variable that researchers measure to evaluate if it changes as a direct result of the manipulation of the independent variable.

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- Control Group
- Experimental Group
- Independent Variables
- Dependent Variables
- Participants must be assigned randomly to experimental and control groups.
- Between and Within-Group Designs
- Internal Validity
- External Validity
- Analog Research

Features of a Typical Experimental Study 

* Experimental hypothesis
* Experimental group
* Control group
* Confederate
* Operational definition
* Independent variable
* Dependent variable
* Random sample
* Random assignment

Basic Experimental Design Components

The primary objective of an experimental study is to determine if a causal relationship exists between different factors. This involves investigating whether intentionally changing one variable results in a measurable change in another variable.

The Core Aim of Experimental Research

A variable is any quantity, quality, or characteristic that can change or vary across different individuals, situations, or over time. In psychological research, some variables are straightforward and simple to measure, such as age or height, while others are more complex and require careful operational definition to be studied empirically.

Variable

An experiment is a specific type of research study designed to determine if a meaningful relationship between two variables is causal in nature. By utilizing statistical analysis to support these causal conclusions, experiments serve as one of the most common and valuable tools in psychological research.

Experiment

Trull , T. J., &amp; Prinstein , M. J. (2013). Research Methods in Clinical Psychology . In Clinical Psychology (Eighth, pp. 93–124). Textbook, Wadsworth Cengage Learning . 

Clinical Psychology Eighth Edition 

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

https://kpu.pressbooks.pub/psychmethods4e/

KPU Research Methods in Psychology - 4th American Edition

Comparisons might be made on the same patient at different points in time

Within-Group Design

When the results of an experiment can be applied to the general population.

External Validity

Studies conducted in the laboratory, where control is easier to exert, but whose conditions are said to be “analogous,” or comparable, to real life. 

Analog Research

In experimental research, an independent variable is the presumed cause in a cause-and-effect relationship. It is the specific factor that a researcher systematically manipulates or varies to observe its impact on another variable. While experiments require manipulation, in some non-experimental or factorial designs, an independent variable may simply be measured.

Independent Variable

Dependent Variable

In an experiment, the experimental group consists of the participants who are exposed to the experimental manipulation. This group receives the specific treatment or level of the independent variable that the researcher is investigating to observe its effect on the dependent variable.

Experimental Group in Research

In an experimental study, a control group consists of participants who do not receive the experimental treatment or manipulation. This group serves as a baseline to compare against the experimental group, allowing researchers to determine if the treatment was effective. In clinical research, if a treatment is found to be beneficial, the ethical principle of seeking justice dictates that participants in the control group should be offered the treatment after the study concludes to ensure fair distribution of benefits.

Control Group in Research

A between-subjects experiment is an experimental design approach wherein each participant is exposed to only a single level of the independent variable. This method differs fundamentally from within-subjects designs, as individuals are tested in just one specific condition rather than across all experimental variations.

Between-Subjects Experiment

A hypothesis is a specific prediction regarding the outcome of a particular scientific study. In the hypothetico-deductive method, hypotheses are derived directly from broader theories and are then tested empirically to support or reevaluate those theories. Importantly, disconfirming a hypothesis does not necessarily mean that the underlying theory from which it was derived has been disproved.

Hypothesis

A confederate in a study refers to an individual who is completely aware of the goals of the experiment. They work with the researcher of the study. The purpose of having a confederate in an experiment (specifically, a social experiment) is to have them manipulate a social situation.

Confederate

In an ideal two-group experimental design, the only difference between the experimental and control groups is their exposure to the experimental manipulation. Both groups go through all phases of the study, but they experience different levels of the independent variable. The researcher then measures any changes produced in the dependent variable for each group and analyzes the collected data statistically to determine if there are meaningful differences between them.

Basic Two-Group Experimental Design

Random assignment is the primary method used to control extraneous variables across experimental conditions. It involves using a chance-based procedure to determine which participants are placed into which conditions. Strictly speaking, it requires that every participant has an equal probability of being placed in any condition and that each individual's assignment is completely independent of the others.

Random Assignment

A researcher wants to test if a new public speaking workshop reduces anxiety. They measure the anxiety levels of 50 volunteers before they participate in the workshop. A week after the workshop is completed, the researcher measures their anxiety levels again and finds that the average anxiety level has decreased. The researcher concludes the workshop is effective. What is the most significant flaw in this study's design?

An operational definition defines a psychological variable in terms of the exact procedures used to measure or observe it. Because most variables are abstract constructs that cannot be directly observed (e.g., stress), researchers must transform these conceptual definitions into concrete, quantifiable forms. For instance, stress could be operationally defined as a score on a standardized questionnaire, the concentration of cortisol in saliva, or the number of recent stressful life events experienced.

Operational Definition

Simple random sampling is a method for obtaining a study sample where every single member of the target population has an equal chance of being selected. While this approach is effective for ensuring a representative sample, it is often difficult or impossible to achieve in psychological research because populations are rarely defined clearly enough to give everyone an equal selection chance.

Simple Random Sampling

A team of researchers is planning a study. Which of the following research goals best exemplifies the primary purpose of an experimental investigation?

A constant is a property or quantity that does not vary across individuals or situations, such as the speed of light. Because constants do not change, they are not the focus of psychological research questions, which instead seek to understand phenomena that vary.

Constant

A quantitative variable is a type of variable that represents a measurable quantity, typically assessed by assigning a numerical value to each individual. Common examples in psychological research include a person's height, level of talkativeness, number of siblings, or score on a depression scale.

Quantitative Variable

A categorical variable is a type of variable that represents a characteristic or quality, typically assessed by assigning a descriptive category label to each individual rather than a number. Examples include a person's chosen major, nationality, occupation, or whether they are receiving psychotherapy.

Categorical Variable

An abstract construct, also referred to as an intangible variable, is a psychological characteristic or internal state that cannot be directly observed, such as self-esteem, mood, or a behavioral intention. Because psychological research relies on empirical data, researchers must develop specific methods to transform these intangible concepts into quantifiable variables so they can be measured and studied.

Abstract Construct

In research, a population is the entire group of individuals that the researchers seek to draw conclusions about based on their findings from the sample. 

Population

In research, a population is the entire, often very large, group of individuals that researchers are interested in studying and drawing conclusions about. Depending on the researcher's goals, a population could be as broad as all human beings or as specific as all American teenagers, children with autism, or professional athletes.

To illustrate how quantities and qualities can vary across individuals or situations, consider the students enrolled in a university course. The physical height of these students serves as a clear example of a variable because it differs from one individual to another. Similarly, their chosen major is also a variable, provided that the class consists of students who have declared different fields of study. These illustrations demonstrate how commonly variations occur in the world.

Example of a Variable: Height and Chosen Major

The distribution of a variable describes how individual scores or values are spread across the different levels or categories of that specific variable within a dataset.

Variable Distribution

In psychology, a construct is a complex variable that defies direct observation or straightforward measurement—such as an attitude, ability, personality trait, or emotional state. These variables cannot be seen directly because they represent broad behavioral tendencies rather than isolated actions, and they involve hidden internal processes like specific feelings, thoughts, and nervous system activities. Ultimately, a construct acts as a theoretical summary that encapsulates these intricate sets of internal and external processes.

Psychological Construct

Measurement is the process of systematically assigning scores to individuals or objects so that these scores accurately represent a specific characteristic of interest. Crucially, this broad concept does not limit measurement to the use of specific physical instruments or tools; rather, it requires any methodical procedure that yields a representative score.

Measurement

A participant variable, also known as an individual difference, is a type of extraneous variable derived from the pre-existing characteristics of the individuals involved in an experiment. Examples of these variables include demographic factors such as gender, as well as personal attributes or habits like diet and writing ability. Because these individual differences are likely to have their own independent effect on the dependent variable, they must be controlled to prevent them from obscuring the effect of the experimental manipulation.

Participant Variable

Psychological measurement is the systematic empirical process of quantifying abstract variables and constructs—such as moods, self-esteem, or behavioral intentions—to facilitate scientific analysis. By utilizing standardized tools and methodologies, researchers can translate intangible psychological characteristics into objective, numerical data that can be rigorously evaluated and studied.

Psychological Measurement

The distribution of a variable describes how scores or values are spread out across the different levels or categories of that specific variable.

Distribution of a Variable

Which of the following best describes a variable in psychological research?

To manipulate an independent variable means to systematically change its level so that different groups of participants are exposed to different levels of that variable, or the same group of participants is exposed to different levels at different times. This active manipulation is a fundamental requirement of an experiment and is used to create distinct conditions for comparison.

Experimental Manipulation

A within-subjects experiment is an experimental design strategy where every participant is exposed to all levels of the independent variable. This approach contrasts with between-subjects designs by testing the exact same individuals across every experimental condition instead of assigning them to just one.

Within-Subjects Experiment

A pilot test is a small-scale preliminary study conducted prior to a full experiment to ensure that a new research procedure functions exactly as planned. By running this trial, researchers can identify logistical issues, clarify instructions, and refine their methodology before committing resources to the main investigation.

Pilot Test

Experimental control is the fundamental process by which researchers hold extraneous variables constant throughout a study. Because extraneous factors—such as individual participant differences or situational contexts—are likely to have an unintended effect on the dependent variable, they make it difficult to separate their impact from the true effect of the manipulated independent variable. By actively controlling these outside variables and preventing them from fluctuating across conditions, researchers can isolate the independent variable and confidently attribute any changes in the dependent variable to the experimental manipulation.

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