Q: What is the best format for the data?
A: Formats that can be opened using free software are better. A good format for small samples is .csv, for medium to large samples use .xlsx or .ods say. Very large samples should be in a database.
However, ensure that all metadata is also provided, either in separate sheets or separate files. This includes the source of the data and a description of how it was collected, detailed descriptions of all variables, descriptions of categories for categorical variables, any codes and jargon used.