Random Assignment
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.
0
1
Tags
Social Science
Empirical Science
Science
Ch.1 Introduction to Psychology - Psychology @ OpenStax
OpenStax
Psychology @ OpenStax
Ch.2 Psychological Research - Psychology @ OpenStax
OpenStax Psychology (2nd ed.) Textbook
Psychology
KPU
Research Methods in Psychology - 4th American Edition @ KPU
Related
Hypothesis
Independent Variable
Dependent Variable
Basic Two-Group Experimental Design
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?
Operational Definition
Simple Random Sampling
Confederate
Confederate in Research
Random Assignment
Advantages of Between-Subjects Experiments
Independent-Samples t-Test
One-Way ANOVA
Within-Subjects Experiment
Matched-Groups Design
Examples of Between-Subjects Experiments
Example of Lack of Context in Between-Subjects Designs
Combining Between-Subjects and Within-Subjects Designs
Equivalent Groups
Nonequivalent Groups
Which of the following best describes a between-subjects experiment?
In a between-subjects experiment, researchers test each participant across every level of the independent variable to directly compare their individual responses.
A researcher is conducting a between-subjects experiment to test if '8 hours of sleep' versus '4 hours of sleep' affects cognitive performance on a memory task. Arrange the steps of this specific study in the correct chronological order.
A researcher investigates whether a new font improves reading speed. They assign 50 participants to read a text in 'Times New Roman' and another 50 participants to read the same text in 'OpenDyslexic'. Match each aspect of this study to the structural logic of a between-subjects experiment.
You are tasked with creating a research protocol to investigate whether a 'Gamified' exercise app increases user motivation more than a 'Standard' exercise app. To avoid 'carryover effects'—where the experience with one version of the app might influence the user's perception or performance with the other—you decide to implement a between-subjects experiment. Which of the following plans should you develop to successfully fulfill this design requirement?
A researcher is evaluating whether to use a within-subjects or a between-subjects design for a study on a permanent educational intervention. They determine that a(n) _____ design is the only valid choice because the intervention results in an irreversible change, making it impossible for the same participants to serve in both the experimental and control conditions.
An experimental design in which each participant is exposed to only a single level of the independent variable is called a(n) _____ experiment.
A clinical researcher measures each participant's stress level at three time points: before a mindfulness program begins (Week 0), after four weeks of training (Week 4), and after eight weeks of training (Week 8). Every participant completes the same single program. The researcher argues that this is a between-subjects design because each participant is assigned to only one program. This argument is correct.
A researcher studies whether type of reward (monetary payment, verbal praise, or no reward) affects how long elementary school children persist on a difficult puzzle. One group receives money after each puzzle attempt, a second group receives verbal praise, and a third receives nothing. No child participates in more than one condition. Match each term to the description that correctly identifies its role in this study.
A research team wants to test whether a new anti-anxiety drug (Drug A), an established drug (Drug B), or a placebo reduces self-reported anxiety in adults with generalized anxiety disorder. They must design the study and analyze the data responsibly. Arrange the following decisions and actions in the order that best reflects sound research practice for a between-subjects experiment.
Define a between-subjects experiment. In your definition, clarify how participant exposure to the independent variable distinguishes this design from a within-subjects design.
Explain why this study is classified as a between-subjects design. Additionally, explain how stable individual differences among the participants in the separate groups affect the within-groups variability () and the resulting statistic in the One-Way ANOVA.
Suppose you are designing a between-subjects experiment to test the effects of two different teaching methods on student learning. What must you do when assigning participants to the two conditions, and what is the primary methodological reason for doing so regarding participant variables?
Placebo
Random Assignment
What is the primary purpose of experimental control in a research study?
Match each component of experimental control with its specific role in a psychological experiment to demonstrate how researchers isolate causal effects.
A cognitive psychologist is studying the effect of word length on memory. To maintain experimental control, the psychologist ensures that all participants see the words on the same computer screen, at the same distance, and for the same duration of time.
A researcher is studying the effect of a new 'Focus App' on student productivity. To ensure that the app is the actual cause of any improvement, the researcher must apply experimental control. Arrange the steps of this process in the correct logical order to demonstrate how control isolates the independent variable.
The primary purpose of experimental control is to prevent extraneous variables from fluctuating across the different conditions of a study.
A researcher investigating a new study technique ensures that all participants take their practice tests in the same quiet room at the same time of day. Which statement best interprets the scientific rationale for this application of experimental control?
A researcher claims that a specific exercise program increases mental clarity, but they fail to hold the participants' daily caffeine intake constant across the different groups. Because the researcher did not maintain experimental control over this outside factor, a scientific evaluator would conclude that the researcher cannot make a valid causal _____ regarding the program's actual effect.
A cognitive psychologist is investigating how different lighting levels affect reading comprehension. Match each element of this study to the correct variable type or control function to show how the researcher isolates the causal effect.
In a study testing a new memory drug, the researcher tests the drug group in the morning and the placebo group in the afternoon. Because time of day was allowed to fluctuate across conditions, the researcher failed to maintain experimental control over this _____, making it difficult to isolate the true effect of the drug.
Arrange the steps in the logical order a researcher must follow to evaluate and establish experimental control in a study testing a new reading application.
Based on the concept of experimental control, define what this process entails and state its primary purpose. Additionally, identify the two broad categories of extraneous factors mentioned that can have an unintended effect on the dependent variable if not controlled.
Applying the concept of experimental control, explain why the researcher cannot confidently conclude that the study environment caused the difference in reading comprehension. Diagnose the specific extraneous variables that were allowed to fluctuate and explain how this failure prevents the researcher from isolating the independent variable.
A researcher is studying the effect of a new cognitive training app on memory recall. If they want to apply experimental control to the situational context of room temperature, what concrete action must they take, and why is this action necessary according to the concept of experimental control?
Cause-and-Effect Relationship
Example of a Causal Claim in Experimental Research
Random Selection in Experiments
Random Assignment in Experiments
Logic of Causal Inference in Controlled Experiments
A researcher reviews the findings from four different studies. Which of the following conclusions could only have been drawn from a study using an experimental design?
Blinding in Experiments
Conditions for Causal Statements in Experiments
Random Assignment
Learn After
Role of Random Assignment in Ensuring Group Comparability
A researcher wants to test if a new type of energy drink improves performance on a memory test. After recruiting 100 volunteers, which of the following procedures is the most effective way to create an experimental group (receives the energy drink) and a control group (receives a placebo)?
Block Randomization
Fallibility of Random Assignment
Random Assignment vs. Random Sampling
Modified Random Assignment
Software for Randomization
Using a Random Number Generator to Understand Randomization
Example of Simple Random Assignment
What is the primary function of random assignment in an experimental design?
A researcher assigns the first 30 participants who arrive at the lab to the treatment group and the next 30 participants to the control group. This method successfully achieves random assignment because both groups have an equal number of participants.
Match each core requirement or outcome of random assignment with the description that best explains its role in ensuring a fair experiment.
Ensuring Randomness and Statistical Power in Randomized Controlled Trials
In a between-subjects experiment, random assignment is the primary tool for establishing internal validity. Sequence the following steps to represent the logical progression from the initial procedural action to the final scientific conclusion.
A research team is designing an automated system for a study where they will compare three groups: Condition A, Condition B, and Condition C. To construct a protocol that strictly satisfies the definition of random assignment, which logic should the team program into their system?
Strictly speaking, random assignment 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.
To effectively control for extraneous variables, researchers must follow a specific procedural logic. Arrange the following steps to correctly sequence the process of random assignment for participants in an experiment.
A researcher evaluates an experimental protocol where participants who arrive at the lab in pairs are always assigned to the same condition to ensure they remain together. Methodologically, this protocol is flawed because it fails to satisfy the strict definition of random assignment, which requires that every individual's placement must be completely _____ of the others.
Match each component or requirement of random assignment with its correct description based on the strict methodological definition.
A researcher evaluates an experimental protocol where participants who arrive together are always placed in the same group. This protocol violates the strict definition of random assignment because each participant's assignment is not _____ of the others.
According to the formal definition of random assignment, what two conditions must be met when placing participants into experimental conditions?
True or False: The primary purpose of random assignment in an experiment is to select a representative sample of participants from the broader target population.
A researcher is planning a between-subjects experiment to test a new study-skills program. Match each procedural scenario with its methodological classification or consequence regarding random assignment.
A researcher plans to assign 40 participants to either an 'experimental' or a 'control' group. To ensure exactly equal group sizes, they assign participants in pairs: for each pair of consecutive participants, the researcher flips a coin. If the coin lands on heads, the first participant goes to the experimental group and the second to the control group; if it lands on tails, the first goes to the control group and the second to the experimental group.
While every participant still has a 50% chance (a probability of 0.5) of being placed in either group, this method is not strictly random assignment because the second participant's group is entirely determined by the first participant's assignment. This procedure violates the strict requirement of ____.
A research team is designing an experiment and evaluating four different participant assignment procedures to control for extraneous variables.
Arrange the following procedures in order from the most methodologically sound (strict adherence to both criteria of random assignment) to the least methodologically sound (not random assignment / highest threat to internal validity).
Which of the following is the primary methodological function of using random assignment in an experimental research study?
Which of the following statements best explains how random assignment successfully controls for extraneous participant variables across experimental conditions?
A researcher is conducting an experiment with 40 participants and two conditions (Group A and Group B). To ensure that both groups have exactly 20 participants, the researcher flips a coin for each participant as they arrive. However, once Group A reaches its maximum capacity of 20 participants, all subsequent participants are automatically assigned to Group B.
True or False: This procedure is a valid random assignment because a coin flip was used to determine group placement.
A researcher wants to test if a new public speaking workshop improves confidence. They advertise the workshop to 100 students. The first 50 students who sign up are placed in the workshop group, while the last 50 to sign up are placed in a control group that receives no workshop. After the workshop, the first group reports significantly higher confidence than the control group. What is the most critical flaw in this study's design that prevents the researcher from concluding that the workshop caused the increase in confidence?
A research team is designing different experiments but is struggling to implement true random assignment. Match each researcher's participant-assignment scenario with the specific methodological violation or consequence it has on experimental control.
An educational psychologist is evaluating two proposed participant-assignment methods for a between-subjects experiment designed to compare a new reading intervention against a standard curriculum.
Method A: The researcher uses a computerized random number generator to assign each student to either the intervention or control group. This results in students in the intervention group and students in the control group.
Method B: The researcher assigns students in pairs; for each pair, they flip a coin to put the first student in either the intervention or control group, and automatically place the second student in the other group. This results in exactly students in each group.
When evaluating these two methods in terms of strict experimental control, internal validity, and the criteria of random assignment, which of the following judgments is methodologically correct?