You compare the effect sizes with the measurement uncertainty. For example if I wanted to conclude that a solenoid worked I could correlate piston position with applied voltage, and I might not need to worry about statistics because the motion of the piston is very large compared to the uncertainty in my implicit visual measurement of its movement. Admittedly that's not how anybody thinks intuitively, but it is correct.
>"For example if I wanted to conclude that a solenoid worked I could correlate piston position with applied voltage"
No one would do this, its once again a "rudimentary science" behavior. People have figured out what we need to know to get the exact relationship between voltage and position.
