It is difficult to draw convincing conclusions from observational studies. There are many potential pitfalls and many research decisions for which clear methodological advice does not exist. The reporting burdens are, therefore, far heavier than for studies that can proceed largely by well-accepted recipes. Beyond the reporting suggestions discussed above, there will often be additional matters of a study-specific nature that will need to be disclosed. Good practice depends on reporting anything about the data collection and analysis that could materially affect the findings.