What type of statistical test should I use?

For some data in a survey I work on, I have two sets of current year-

prior year ratios. I have a set of current-year prior year ratios for

numbers that ended up being changed from what was originally reported

by the data respondent (around 500 numbers in this set) and another

set of current-year prior year ratios for numbers that were not

changed from what was originally reported (around 800,000 numbers in

this set). I wanted to do a statistical test to determine if the

average current year-prior year ratio of the numbers that were changed

on the survey are significantly different from the average current

year prior year ratio of numbers that were not changed. What kind of

test should I use? Also wanted to know if it might be better to

separate the current-year prior year ratios into ratios that increased

from the prior year vs. decreased from the prior year and run tests on

each group?? Thanks for any advice...

Julie