Again, the key variable of interest for Goble and his colleagues was athletes' balance which was measured as the number of centimeters of sway over...

Again, the key variable of interest for Goble and his colleagues was athletes' balance which was measured as the number of centimeters of sway over the course of a 20-second trial.

If another researcher wonders if the number of centimeters of sway during a trial really measures balance, this researcher is wondering about which type of validity?

Internal validity

Construct validity

External validity