Final answer:
Individual differences (assignment bias) can affect internal validity and introduce confounding variables. Lurking variables must be accounted for, and random assignment is essential in preventing systematic group differences in experimental design.
Step-by-step explanation:
Individual differences (assignment bias) are a threat to internal validity and can produce confounding variables in the scores. Assignment bias can lead to a situation where the participants in different groups may not be equivalent at the beginning of a study due to non-random assignment. This can jeopardize the internal validity of the research, making it difficult to ascertain whether outcomes are truly due to the experimental intervention or due to the pre-existing differences between groups.
When analyzing instances such as SAT score disparities between males and females, it's important to consider lurking variables that may be influencing outcomes. Cultural factors, educational experiences, societal expectations, and a host of other issues can potentially explain the observed differences in test scores, rather than genetic factors alone.
Therefore, researchers need to carefully plan their experimental designs to control for such biases and ensure the credibility of the study. Random assignment is a tool often used to prevent such biases, as it decreases the chance that the groups will have systematic differences not related to the study's experimental conditions.