You can measure something consistently wrong every single time—that's reliable but invalid. Or you can hit the true value once in a scattered pattern—that's valid but unreliable. Psychology research demands both, but they're independent properties that need separate assessment. Drag the slider to see how confounding variables erode internal validity even when measurements stay reliable.
External validity determines whether your findings travel beyond the laboratory walls. Ecological validity asks if your carefully controlled experimental task resembles anything people actually do in real life—does a word-list memory task reflect how students study for exams? Population validity questions whether your sample of 120 undergraduate psychology students tells us anything about decision-making in middle-aged executives, rural farmers, or elderly hospital patients. High internal validity often comes at the cost of external validity because tight experimental control creates artificial situations.