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An experiment involves manipulating one or more variables to observe the effect on another variable, often with random assignment to treatment groups. In contrast, an observational study involves observing subjects without manipulating any variables, simply recording data as it naturally occurs. Determining whether a study is experimental or observational is crucial for understanding the nature of the conclusions that can be drawn.

Sampling bias occurs when the sample collected is not representative of the population intended to be analyzed, often due to non-random selection methods. In the context of surveys, voluntary response bias is a common form of sampling bias, where individuals self-select to participate, potentially skewing results. Recognizing sampling bias is essential for evaluating the reliability and validity of survey findings.

A voluntary response sample is a type of non-probability sampling where participants choose to be part of the sample. This method often leads to biased results because those who feel strongly about the topic are more likely to respond, which may not reflect the views of the general population. Understanding this concept helps in assessing the limitations of survey data and the generalizability of its conclusions.