A researcher wants to test if a new 'mind-mapping' study technique improves exam scores. They recruit 50 students, have them all use the mind-mapping technique for one week, and then measure their scores on a final exam. The researcher concludes that since the average score was 85%, the technique is effective. What is the most significant flaw in this research design?

In a classic 1952 article, researcher Hans Eysenck challenged the assumed effectiveness of psychotherapy by evaluating the results of existing pretest-posttest designs. Although the original clinical studies showed patient improvement after receiving therapy, Eysenck compared these results to archival data from state hospitals and insurance companies for untreated patients. He found that both the treated and untreated groups recovered at similar rates. This highlighted that the improvements observed in the treated group were likely due to spontaneous remission rather than the psychotherapy itself, underscoring the absolute necessity of including a proper control group to accurately measure treatment efficacy.

Eysenck's 1952 Psychotherapy Effectiveness Study

What is the primary purpose of a control group in an experimental study?

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.

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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 

The moral principle of seeking justice requires researchers to treat all individuals fairly and ensure an equitable distribution of both the risks and benefits associated with scientific research. On an individual level, this means fairly compensating participants and offering effective treatments to control groups at the study's conclusion. On a broader societal level, it demands that historically marginalized or vulnerable populations—such as institutionalized individuals, disabled people, or ethnic minorities—do not bear a disproportionate burden of research risks, a standard established in response to past historical atrocities.

Seeking Justice

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

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 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

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

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

The Tuskegee syphilis study, conducted by the US Public Health Service from 1932 to 1972, is a tragic historical example of extreme injustice in scientific research. The study involved poor African American men in Alabama who were misled into believing they were receiving treatment for 'bad blood' while actually being observed for the untreated progression of syphilis. The researchers deliberately denied the men treatment even after penicillin became the standard cure, clearly violating the ethical mandate to treat participants fairly and highlighting the urgent need to protect marginalized groups from disproportionate research risks. The profound betrayal of these men was formally acknowledged in 1997 when President Bill Clinton issued a public apology on behalf of the US government, emphasizing how the participants had been exploited without their knowledge or consent.

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