Một hình thức của lỗi khó phát hiện hơn là hiện thân của một ảo tưởng hợp lý được biết đến như đơn yêu cầu principii, hoặc đối số tròn. Khi một kết luận là hình tròn, thường là phương pháp đã thừa nhận kết luận ngầm ở cơ sở. Trong logic biểu tượng, hình thức suy luận được gọi là modus ponens là bị hỏng trong lý luận tròn vào lặp: Nếu q ⇒ p và q là đúng kết luận q lỗi ở đây là sự thật của q không phải là kéo theo sự thật của trang. | Chapter 11 Circularity Another form of error more difficult to detect embodies a logical fallacy known as petitio principii or the circular argument. When a conclusion is circular usually the methodology has assumed the conclusions implicitly in the premises. In symbolic logic the form of inference called modus ponens is corrupted in circular reasoning into the tautology If p q and q is true conclude q The error here is that the truth of q is not entailed by the truth of p. One way of testing for circularity is to see if a methodology generates the same results with random data as with the real data. This together with the initial premise that p q is equivalent to setting p q and p q If the conclusion is still true . the same results are achieved using random numbers instead of the supposed signal then it is highly likely the model entails the result q irrespective of the conditions. Climate prediction Circularity is illustrated on the climate reconstruction model used in a previous chapter where randomly generated sequences are used to develop predictions of past climate. We examine the potential for circularity via the selection of series or cherry picking for series highly correlated with temperature. The process through which temperature reconstructions are developed from tree-rings is to collect a number of tree-ring widths or densities from cores of large trees older than the instrumental temperature record. These series are 173 2007 by Taylor and Francis Group LLC 174 Niche Modeling 0 500 1000 1500 2000 proxy year FIGURE A reconstruction of temperatures generated by summing random series that correlate with temperature. normalized to reduce the effect of promiscuous early growth. The series are then tested for correlation with temperature. Those that are best correlated with the instrumental temperature record are selected either prior to analysis or through differential weighting in statistical techniques. The selected series are then .
