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

Basic Experimental Design Components

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

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

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 confederate is a person who is aware of the experiment and works for the researcher. They are used to manipulate social situations as part of the research design, while the true, naïve participants believe that confederates are uninformed participants in the experiment.

Confederate

A confederate is an individual who is aware of an experiment's true purpose and works for the researcher to manipulate social situations. While confederates act as part of the experimental design, true, naïve participants believe they are simply fellow, uninformed subjects.

Confederate in Research

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?

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