The concept of validity in psychological assessment is crucial for making sure measurement tools are accurate. Different types of validity evidence are gathered to support the claim that a test is valid. There is a shift towards a unified approach to validity, focusing on the overall evidence gathered. The way we measure psychological phenomena and the theories behind them affect how we determine validity. It's important to consider all available evidence, including issues of bias and fairness, when using test scores to make decisions. Differences in how we measure and validate tests can lead to varying results, even when measuring the same thing.