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

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

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.

Dependent Variable

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

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

University of Chicago

Columbia University

Google

Experimental research is a method that involves a tremendous amount of control over variables of interest. It utilizes randomized assignment of participants to conditions and systematic manipulation of an independent variable to observe its effects on a measured dependent variable, with the objective of drawing causal inferences.

Experimental Research

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

* Double-blind study
* Single-blind study

Types of Experimental Research 

Basic Experimental Design Components

After an experiment's data has been gathered from both the experimental and control groups, a statistical analysis is performed to interpret the results. The purpose of this analysis is to ascertain whether any observed differences between the groups are meaningful or simply the result of random chance.

Interpreting Experimental Findings in Psychology

Many researchers in psychology want to share their findings with their peers and other scholars in the field. Generally, researchers will publish peer-reviewed journal articles. 

Reporting Research in Psychology

A significant limitation of experimental research stems from its reliance on a controlled, laboratory environment. This artificial setting raises questions about ecological validity, meaning researchers must be cautious when generalizing findings, as behaviors observed in the lab may not accurately reflect how individuals act in their natural, real-world environments.

Weakness of Experimental Research: Artificial Settings

A major limitation of the experimental method is that ethical considerations can prohibit researchers from investigating many important psychological questions. If manipulating a variable could cause harm or distress, an experiment cannot be ethically conducted, forcing researchers to use other methods.

Ethical Constraints in Experimental Research

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

The main advantage of experimental research is its unique ability to determine cause-and-effect relationships. By systematically manipulating an independent variable while controlling for extraneous factors, researchers, including those in developmental psychology, can confidently make causal statements about the impact of specific variables on a given process.

Primary Strength of Experimental Research: Establishing Causality

A researcher wants to test if a new note-taking strategy improves exam performance. They teach the new strategy to their morning class and the traditional strategy to their afternoon class. At the end of the unit, the morning class scores significantly higher on the exam. The researcher concludes that the new strategy *causes* better exam performance. Which of the following statements best analyzes the validity of this conclusion?

Falsifiability is a defining characteristic of any scientific claim, meaning it must be expressed in a way that allows for potential observations that would count as evidence against it. As argued by philosopher Karl Popper, if a claim cannot be tested and potentially proven wrong by systematic observation, it does not address an empirical question and is therefore considered pseudoscientific rather than scientific.

Falsifiability

An example of an experimental design involves manipulating room lighting to examine its effects on workers' productivity. In this scenario, the lighting conditions (bright versus dim lights) represent the independent variable, while the workers' productivity is the measured dependent variable. If loud noise is present only when the lights are bright, that noise becomes a confounding variable because it varies systematically with the lighting, providing an alternative explanation for any productivity changes. However, if the noise is present equally under both lighting conditions, it is merely an extraneous variable that does not disrupt the ability to make causal conclusions about the lighting.

Example of an Experiment: Lighting and Worker Productivity

A field experiment is a type of field study where the researcher actively manipulates an independent variable in a natural setting while controlling extraneous variables as much as possible. Depending on the level of control achieved, these studies can yield high levels of both internal and external validity.

Field Experiment

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

There are many situations where a researcher cannot actively manipulate an independent variable for practical or ethical reasons, making a true experiment impossible. For example, a researcher cannot ethically manipulate whether individuals suffer a significant early illness to study its effect on hypochondriasis. When active manipulation is not possible, researchers must investigate the relationship using nonexperimental approaches.

Inability to Manipulate Variables

In experimental research, maintaining an organized and detailed record log is crucial. Researchers typically prepare a written sequence of experimental conditions in advance. As each subject is tested in their corresponding condition, researchers should record basic demographic details, the testing date, time, and location, as well as the presiding experimenter's name in this log. It is also important to document any unusual events—such as a participant becoming confused or uncooperative—or any spontaneous questions that emerge during the session. Keeping such comprehensive notes enables researchers to accurately address future inquiries about specific sessions and to statistically analyze potential effects, such as demographic differences or variations caused by different experimenters.

Experimental Record Keeping

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

Quasi-experimental research is a methodological design that incorporates some, but not all, of the essential features of a true experiment. While researchers using this approach may introduce a treatment or comparison condition, they frequently fail to use random assignment to place participants into distinct groups or omit counterbalancing to control for potential order effects. Consequently, while it offers more control than purely correlational studies, quasi-experimental research generally possesses lower internal validity than true experimental research.

Quasi-Experimental Research

Experimental, quasi-experimental, and non-experimental (correlational) research vary systematically along a spectrum of internal validity. True experimental research generally possesses the highest internal validity because it utilizes the manipulation of an independent variable and strict control over extraneous variables to confidently rule out alternative explanations. In contrast, non-experimental research ranks lowest in internal validity because it fundamentally lacks variable manipulation and control. Quasi-experimental research occupies the middle ground; it incorporates some structural features of an experiment but lacks others, such as the random assignment of participants.

Comparison of Internal Validity Across Research Designs

Survey research is a versatile methodology utilized to investigate a wide range of basic and applied research questions. It is predominantly used as a non-experimental research design to describe single variables, such as estimating the prevalence of mental disorders, or to identify statistical relationships among naturally occurring variables. Additionally, surveys can function as a data collection method within experimental research to test specific hypotheses concerning causal relationships between variables. When deployed with large and diverse samples, these survey-based experiments provide a valuable complement to traditional laboratory studies.

Applications of Surveys

A laboratory experiment is a research study conducted in a highly controlled environment. Because researchers can manipulate variables and minimize outside influences, laboratory experiments typically possess high internal validity, enabling researchers to draw strong causal conclusions.

Laboratory Experiment

Single-subject research, frequently referred to as small-$$n$$ design (where $$n$$ represents the statistical symbol for sample size), is a quantitative methodology that involves studying a small number of participants and focusing closely on each individual's behavior. Despite its name, this approach typically investigates between two and ten participants rather than just one. Serving as a crucial alternative to group research, particularly in applied areas of psychology, single-subject research seeks to comprehend objective behavior by utilizing strict experimental manipulation and control to collect highly structured data that is analyzed using quantitative techniques.

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