If I want to show the comparison between rate in 2010 Jan and 2009 Jan, which of the following should I use?
- Comparison of rate between 2010 Jan and its prior month.
- Comparison of rate between 2010 Jan and its previous month.
In my opinion, neither previous nor prior work in this context for what you want to express, because both expressions imply December 2009.
Also, ‘between’ is a bit vague, because while the context implies you are comparing the rates of the two months, ‘between’ carries the idea of comparing the rates for the whole period between those two months.
Why not simply ‘Comparison of rates: Jan 2010 and Jan 2009’? It is not especially clever, but it is shorter than the two phrases you propose.