A researcher is interested in the relationship between vocabulary and school achievement in Grade 1. The researcher decides that to control for IQ, which also is expected to influence achievement in Grade 1. The researcher takes a group of first graders and measures them on vocabulary, achievement, and IQ. Then the researcher statistically examines the relationship between vocabulary and school achievement, controlling for IQ. What is the name of this control technique?
partial correlation
holding the extraneous variable constant
matching
random assignment
