Abstract:The logic of experiments is discussed, and three common mistakes in designing and interpreting experiments among ecologists are analyzed. Researchers sometimes overlook logic problems, while paying too much attention to statistical techniques. A statistically significant difference can demonstrate treatment effect for a well-designed experiment, but it might not for a “bad” experiment. Any extraneous variables that change systematically along with the treatment threaten the internal validity of an experiment. The bias in some cases arises from interdependence between experimental units, which is the case with pseudo-replication, a term coined by S. Hurlbert in 1984. In this paper we review experiments published in one issue each of two of the most influential ecology journals, Journal of Plant Ecology and Acta Ecologica Sinica. Some cases are selected and analyzed to exemplify three mistakes which are commonly made by Chinese ecologists when designing an experiment or interpreting data. They are: (1) simple pseudo-replication, (2) confusing repeated measurements as replicates or temporal pseudo-replication in terms of Hurlbert, and (3) wrongly treating a spatial or temporal pattern as a treatment effect. Among the experiments reviewed, 17.9%-42.9% in Journal of Plant Ecology and 14.3%-42.9% in Acta Ecologica Sinica involved at least one type of the errors mentioned above.