root of the reliability coefficient. For example, if the reliability coefficient for a test of mechanical aptitude is .87, the validity coefficient can be no larger than .93 (which is the square root of .87). What this means in tech talk is that the validity of a test is constrained by how reliable it is. And that makes perfect sense if we stop to think that a test must do what it does consistently before we are sure it does what it says it does. But the relationship is closer as well. You cannot have a valid instrument without it first being reliable, because in order for something to do what
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