Voters are selected by simple random sampling from a complete registered-voter list, and their opinions are recorded. Analyze the sampling frame, selection bias, population generalization, uncertainty, and causal limits.

Analyze sampling in layers: identify whom the frame covers, verify the chance-based entry mechanism, and limit generalization to that frame population. Random sampling reduces systematic selection bias but leaves sampling variability and possible nonresponse. Because sampling determines who enters rather than which treatment they receive, it supports population inference but does not establish causation.