Most studies using modern methods show a moderate positive correlation between brain size and IQ scores.

Nevertheless, interpreting these results is problematic. Why?

a. As children grow older, their brain size increases but their IQ decreases.

b. When people are sleepy or sick, their brain size remains the same but their IQ performance drops.

c. On average, men have larger brains than women, but equal IQ scores.

d. Some parts of the brain are more important for IQ than other parts are.