Question

A researcher interested in finding a simple way to estimate intelligence decides to evaluate skull circumference as a possible indicator of intelligence. he finds that the size of an adult's skull remains the same from one measurement to the next, but he finds that skull circumference is not a very good predictor of intelligence. in this example, skull circumference as a measure of intelligence is

Answer 1

I believe the answer is: reliable but not valid

The measurement of the intelligence is considered as reliable because it initiated with valid logical reasoning and scientific method.
The data at hand is considered as not valid because it only contain one subject of research.