In neuralstudio.ai terminology, “bad” data is data that, while it should be strictly numeric, contains characters which cannot be interpreted as numbers by Java. “Missing” data is exactly that – a field value is empty. In practical terms, that means that a record in a data file contains two consecutive Field Separator characters – such as ,, if comma is specified as the Field Separator. “Unknown” data is data that is marked by a string of characters that you defined as the “Unknown Data Marker” – for example, “N/A”. When neuralstudio.ai encounters the Unknown Data Marker, the field is ignored (treated as missing data), to prevent interpreting the field value incorrectly. “Invalid” data is data that is not valid for domain reasons, such as a numeric value that is unrealistic or not possible in light of the system that generated the value. Checking the validity of data values is not currently supported directly on neuralstudio.ai and must be separately performed on data files.