Psychologists measure intelligence by using standardized tests that produce a score known as the intelligence quotient or IQ. To understand IQ tests, it's important to recognize the key principles behind their construction: validity, reliability, and standardization.

Validity refers to how well a test measures what it claims to measure. An intelligence test should accurately assess intelligence rather than another characteristic, like anxiety. Criterion validity is one way to evaluate this; it looks at how well test scores predict performance in real-world situations, such as job evaluations.

Reliability means the test yields consistent results over repeated administrations. A reliable test will give the same results under similar conditions, ensuring that the measurement is stable over time. However, a test can be reliable without being valid; it might consistently measure something but not necessarily what it is supposed to measure.

Standardization involves creating uniform procedures for administering and scoring the test, along with establishing norms by testing a large, representative group. This process ensures that the test is fair and applicable across different populations, providing benchmarks for interpreting individual scores.

These principles — validity, reliability, and standardization — are crucial in ensuring that IQ tests are both meaningful and fair measures of intelligence.