LEVELS OF EVIDENCE IN STUDIES OF COMPETITION, PREDATION, AND DISEASE

The primary aim of a scientific investigation is to find the most like ly model for a situation out of a host of alternative explanations. Th e strength of evidence provided by anecdote, logical argument, mathema tical modelling, observation, and designed studies (manipulative and o bservational) are discussed and the effectiveness of randomisation and orthogonal designs in separating hypotheses compared. Pseudoreplicati on is shown to be often misunderstood. It consists of two concepts: th e importance of adequate replication and the independence of the sampl ing units. While replication is necessary to separate out the effects of different factors and to provide an error term for inference, contr ary to popular belief independence of sampling units is not necessary. Finally the interpretation of evidence is discussed and the distincti on made between formal and informal generalisation to a population.