This article is part of a series of manuscripts dealing with the incorporation of patient-reported outcomes (PROs) into clinical trials. The issues dealt with in this manuscript concern the common pitfalls to avoid in statistical analysis and interpretation of PROs. Specifically, the questions addressed by this manuscript involve the analysis pitfalls with PRO data in clinical trials and how can they be avoided (e.g.,missing data, multiplicity, null results etc.). The manuscript provides key literature for existing resources and proposes new guidelines.