Sometimes data looks at a glance to be rectangular, but it is structured so messily that it is not analyzable. Such data tends to either be created by manual entry by somebody not experienced in data file preparation.
Common problems that make data files impractical to analyze include:
- Variable names appearing in multiple rows
- Confidential data included in the file
- Data stored as text that should be numbers
- Multiple variables are grouped in a single column.
Data with these properties can be made to be flat, but it tends to involve a lot of work in Excel by somebody with expertise in the preparation of data files.