Final answer:
Schaffer & Emerson's 1964 study on attachment should be assessed for its design, methodology, and influence on later research, considering advancements in social science research and ethics.
Step-by-step explanation:
An evaluation of the validity of Schaffer & Emerson's 1964 study on attachment must consider the robustness of the study's design, the context in which it was conducted, and its influence on later research. Contemporary studies, such as those by McDaniel et al. (1994) on interview validity, and Sonnenfeld (1985) on the Hawthorne Studies, have paved the way for more nuanced and sophisticated approaches to validity in social research. The work by Schaffer & Emerson must thus be assessed in light of later methodological advancements and ethical considerations that have emerged over the years in the field of psychology and social science research. Potential limitations such as sample size, methodology, and generalizability of findings should be considered when evaluating this classic study.