When using or developing experimental and observational methods it is crucial to assess the method performance in an effort to ensure that the information it provides reflects reality. For experimental biologists this often means conducting carefully chosen control experiments with alternative methods or different experimental settings. More rigorous assessment, particularly for high-throughput or large-scale methods, often requires the use of ‘ground truth’ or ‘gold standard’ data sets. But talk to different people and you will get different answers regarding what ‘ground truth’ or ‘gold standard’ data is. This often includes a nice historical explanation of where the term ‘ground truth’ comes from.