Silktide Analytics records all visitor data, but when showing aggregate values we sometimes use samples. For example, say a website had received 10 million views during a period, and you were applying complex filters for location, browser, and so on. Checking all 10 million views could result in unacceptable slow performance, so in such cases, Silktide Analytics might use a smaller sample and extrapolate from that. These samples are large enough that any error is almost guaranteed to be <0.5%.