I have the following data and I want to show that the negative change for group 1 is statistically significantly different from the negative change for group 2. And along the same lines, I also want to compare positive change between group 1 and group 2.

The number of observations is 312 for group 1 and 972 for group 2 and the means are in percentages. The percentages are obviously quite different - but how do I prove that they are statistically significantly different (ideally with p-values)?

Key Indicator-----------First Group------------Second Group

------------------Observations---Mean-----Observations----Mean

1 Grade change

negative----------35-------------11,22%--------2--------------0,20%

no change------149------------47,76%-------316-----------32,51%

positive---------128-------------41,03%-------654-----------67,28%

Is it possible to do a t-test here or what would you recommend? ]]>