Which of the following is a threat to the internal validity of studies using one-group pretest-posttest design?

A) Cohort effects
B) Statistical regression
C) Propensity score matching
D) Selection bias

One-group pretest-posttest design does not include a control group for comparison, making it vulnerable to statistical regression. This occurs when participants with extreme scores in the pretest tend to move toward the mean in the posttest, simply due to chance or natural random variation. This phenomenon can lead to an overestimation or underestimation of the treatment effect, impacting the internal validity of the study. Cohort effects (A), propensity score matching (C), and selection bias (D) are all potential threats to internal validity, but they are not specific to the one-group pretest-posttest design.