Final answer:
Internal validity concerns in a one-group pretest/posttest design stem from the absence of a control group, which means other factors could influence results. Experimenter bias and lurking variables must be controlled, typically through appropriate blinding and experimental design including controls, to ensure reliable results.
Step-by-step explanation:
Internal Validity Concerns in One-Group Pretest/Posttest Design
Internal validity refers to the extent to which a study can demonstrate a direct causal relationship between the treatment and the outcome. The one-group pretest/posttest design raises internal validity concerns because of the absence of a control group to compare against the experimental group. This design can be compromised by factors such as maturation, history, testing effects, or statistical regression, which could influence the outcome independently of the experimental treatment.
In the context of a study investigating the effectiveness of a new math textbook, the researchers have administered pretests and posttests to only one group of students. As a result, the researchers cannot be certain if it is truly the textbook that caused any changes observed in the test results or if other variables are at play. Moreover, if the people scoring the tests are aware of the student's participation in the experiment, experimenter bias could affect the interpretation of the results. To minimize these biases, blinding methods, such as single-blind or double-blind studies, are applied where the scorer or both the participants and the researcher are unaware of group assignments.
The lack of random assignment and the absence of a control group mean that other lurking variables could account for the observed changes in scores, diminishing the study's internal validity. Therefore, replication of findings by other researchers in controlled experimental settings is crucial to validate the efficacy of the textbook.