A subjective extension of time-series data. A time series extended by freehand, also known as bold free hand extrapolation (BFE). This can be done by domain experts, who can use their knowledge as well as the historical data. Most research to date, however, has been done with subjects having no domain knowledge. Interestingly, naive extrapolations have often proven to be as accurate as quantitative extrapolations, perhaps because subjects see patterns that are missed by the quantitative methods. This finding is difficult to believe. In fact, the first paper reporting this finding was soundly rejected by the referees and was published only because the editor, Spyros Makridakis, overrode the referees. The paper (Lawrence, Edmundson and O’Conner 1985) went on to become one of the more highly cited papers in the IJF and it stimulated much useful research on the topic. Judgmental extrapolations can sometimes be misleading. In a series of studies, Wagenaar (1978) showed that people can misperceive exponential growth. For a simple example, ask people to watch as you fold a piece of paper a few times. Then ask them to guess how thick it will be if you fold it another 40 times. They will usually reply that it will be a few inches, some say a few feet, and occasionally someone will say a few miles. But if they calculated it, they would find that it would extend past the moon. Despite the above findings, when the forecaster has substantial domain knowledge, judgmental extrapolation may be advantageous, especially when large changes are involved. For a discussion of principles related to judgmental extrapolation, see Webby, O’Connor and Lawrence (2001).