A study by Rosenthal and Jacobson (1968) involved telling teachers that some of their students were "bloomers" and would achieve rapid academic success within the next year. In fact, these students were no different than any of the other students in the class. At the end of the year, the "bloomers" showed more gains in IQ than the other students. It appeared that the teacher had inadvertently treated the "bloomers" in special ways. This is an example of which of the following?

a. Observer bias
b. Observer effects
c. A masked study design
d. Self-report operationalization