Which African American enjoyed enthusiastic support among whites and blacks when for several months in 1995 he flirted with the possibility of entering the 1996 presidential race?

A researcher studies the relationship between political attitudes and income. The researcher finds that those with higher income are more conservative. The most likely confounding variable is

A) Income. B) Age. C) Weight. D) Health status.

Randomization in selection and assignment can control

A) only one variable at a time. B) for threats to external validity but not for threats to internal validity. C) for many variables simultaneously. D) for threats to internal validity but not for threats to external validity.