Ecological observations are considered scientific evidence if you can show convincingly that they were not received by chance. Before starting a study, you should consider how to distribute and replicate your observations. An introduction to statistical methods is provided for this purpose. We do not provide or discuss the calculations, but we refer you to rapidly developing applications. Fundamental decisions that should be made before collecting data are explained, such as stratification, dependent and independent samples, and sample size. Individual statistical tests are presented by explaining what test can be used for what data type. They can be used either for comparisons of sample series or for testing influencing factors on a selected variable. The latter analysis ranges from simple correlations to complex multivariate procedures. We also provide advice for the presentation of results. For some questions, descriptive indices are sufficient. A frequently used example is the description of diversity. The formulae for calculating some indices are also provided here.