Internal consistency

Internal consistency is when all the parts of something match up nicely with each other. Think of a puzzle – if all the pieces fit together just right, the puzzle is internally consistent. The same thing happens when we try to measure something. If we ask a bunch of questions about a topic (like, "Do you like eating apples?" and "How often do you eat apples?"), the answers should all go together nicely. If someone says they love eating apples but then also says they never eat them, their answers aren't internally consistent. This can make it hard to trust what they're saying. So, we want our measurements to be internally consistent, so we can trust the results.