Some style guides are strict on the particular format for references or whether references must be chronological or alphabetical. However, it is often permissible to number the references. This can be helpful because:
- It is quicker to write and read  or [5-7] than (Jelb 2000) or (Jelb 2000; Carr et al. 2002; Melnok and White 2003), respectively.
- It is easy for the reader to find the reference in the bibliography or reference list, regardless of whether the list is chronological or alphabetical.