Nonequivalent Groups Design

In a between-subjects experiment, what term describes groups that are formed without the use of random assignment and thus possess inherent, pre-existing differences from the outset?

If a researcher assigns participants to conditions based on whether they sign up for a morning or afternoon session, the resulting groups are considered nonequivalent.

A psychologist is conducting several research studies comparing existing groups of people without using random assignment. Match each research scenario to the specific pre-existing difference that would lead the researcher to classify the groups as nonequivalent.

A researcher evaluates a new 'Memory Booster' supplement by comparing a group of students who volunteered for a 6:00 AM trial to a group of students who did not volunteer. Arrange the following statements to logically trace how this lack of random assignment creates 'nonequivalent groups' and leads to ambiguous results.

A clinical psychologist is designing a research protocol to compare the recovery rates of patients in two different psychiatric clinics. To construct a study that specifically utilizes nonequivalent groups, which of the following procedures should the psychologist follow?

In a between-subjects experiment, nonequivalent groups are formed when researchers use random assignment to ensure that the groups are as similar as possible from the outset.

To demonstrate your understanding of group composition in psychological research, match each research-design concept with the statement that best describes it.

A psychologist attempts to test a new memory strategy by comparing students in an 8:00 AM class to those in a 2:00 PM class. When assessing the rigor of this research, a critic would point out that because students were not randomly assigned, the researcher is comparing _____ groups, making any conclusions about the strategy's effectiveness highly questionable.

An educational researcher compares the reading comprehension scores of students in two pre-existing classrooms, where one class receives a new reading intervention and the other does not. In analyzing the design, the researcher notes that because students were not randomly assigned to the classrooms, the groups likely differ on variables such as baseline reading ability and socioeconomic status. Because of these pre-existing differences from the outset, the researcher must analyze these groups as _____ in their study.

A psychologist evaluates a study claiming a new exercise program reduces anxiety. The study compared a group of volunteers who chose the exercise program to a control group who preferred a sedentary lifestyle. Order the steps a critic should take to evaluate the internal validity of the psychologist's claim, starting from identifying the group assignment method to rendering a final judgment on the causal conclusion.

In the context of a between-subjects experiment, define what is meant by 'nonequivalent groups' and explain the specific methodological condition that leads to their formation.

Based on the design of this study, diagnose the group composition. Are the groups in this between-subjects experiment considered equivalent or nonequivalent? Justify your decision based on how the participants were placed into conditions.

A researcher decides to place all participants who arrive before noon into an experimental condition and all participants who arrive after noon into a control condition. Briefly explain why this specific placement method will result in nonequivalent groups.